Display device, manufacturing method of display device, and electronic device

ABSTRACT

A display device in which a peripheral circuit portion has high operation stability is provided. The display device includes a first substrate and a second substrate. A first insulating layer is provided over a first surface of the first substrate. A second insulating layer is provided over a first surface of the second substrate. The first surface of the first substrate and the first surface of the second substrate face each other. An adhesive layer is provided between the first insulating layer and the second insulating layer. A protective film in contact with the first substrate, the first insulating layer, the adhesive layer, the second insulating layer, and the second substrate is formed in the vicinity of a peripheral portion of the first substrate and the second substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/922,658, filed Oct. 26, 2015, now allowed, which claims the benefitof a foreign priority application filed in Japan as Ser. No. 2014-219635on Oct. 28, 2014, both of which are incorporated by reference.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device anda manufacturing method of the display device.

Note that one embodiment of the present invention is not limited to theabove technical field. The technical field of the invention disclosed inthis specification and the like relates to an object, a method, or amanufacturing method. In addition, one embodiment of the presentinvention relates to a process, a machine, manufacture, or a compositionof matter. Specifically, examples of the technical field of oneembodiment of the present invention disclosed in this specificationinclude a semiconductor device, a display device, a light-emittingdevice, a power storage device, a memory device, an input device, aninput/output device, a method for driving any of them, and a method formanufacturing any of them.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A semiconductor element such as a transistor, asemiconductor circuit, an arithmetic device, and a memory device areeach an embodiment of a semiconductor device. An imaging device, adisplay device, a liquid crystal display device, a light-emittingdevice, an electro-optical device, a power generation device (includinga thin film solar cell, an organic thin film solar cell, and the like),and an electronic device may each include a semiconductor device.

BACKGROUND ART

Displays including thin film transistors have been widely spread andindispensable to our life. In addition, these displays are veryimportant for portable displays and have been necessary for portableterminals.

Furthermore, display devices in which a display region (a pixel portion)and a peripheral circuit (a driver portion) are provided in the samesubstrate have been widely used. For example, Patent Document 1discloses a technique of using oxide semiconductor transistors in thedisplay region and the peripheral circuit. When the display region andthe peripheral circuit are formed simultaneously, the manufacturing costcan be reduced.

REFERENCE Patent Document

[Patent Document 1] Japanese Published Patent Application No.2007-123861

DISCLOSURE OF INVENTION

A display device is required to have as large a display region aspossible on a side viewed by a viewer (a display surface side).

In addition, on the display surface side, a frame portion is highlyrequired to be narrow.

However, in the case where a display region becomes large and a frameportion becomes narrow, a driver circuit provided outside the displayregion is positioned further outside the display region, so that thereliability of transistor characteristics of a peripheral circuit maydecrease and the circuit operation may become unstable.

An object of one embodiment of the present invention is to provide adisplay device in which a peripheral circuit portion has high operationstability.

Another object of one embodiment of the present invention is to providea display device with a narrow frame.

Another object of one embodiment of the present invention is to providea lightweight display device.

Another object of one embodiment of the present invention is to providea high-definition display device.

Another object of one embodiment of the present invention is to providea highly reliable display device.

Another object of one embodiment of the present invention is to providea large-area display device.

Another object of one embodiment of the present invention is to providea low-power display device.

Another object of one embodiment of the present invention is to providea novel display device or the like.

Another object of one embodiment of the present invention is to providea method for manufacturing the display device.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects will be apparent fromand can be derived from the description of the specification, thedrawings, the claims, and the like.

One embodiment of the present invention is a display device including afirst substrate and a second substrate. A first insulating layer isprovided over a first surface of the first substrate. A secondinsulating layer is provided over a first surface of the secondsubstrate. The first surface of the first substrate and the firstsurface of the second substrate face each other. An adhesive layer isprovided between the first insulating layer and the second insulatinglayer. A protective film in contact with the first substrate, the firstinsulating layer, the adhesive layer, the second insulating layer, andthe second substrate is formed in the vicinity of a peripheral portionof the first substrate and the second substrate.

Furthermore, a transistor, a capacitor, a display element, alight-blocking layer, a coloring layer, and a spacer can be providedbetween the first surface of the first substrate and the first surfaceof the second substrate.

Furthermore, the protective film can contain an oxide, a nitride, or ametal.

Furthermore, for the protective film, aluminum oxide, hafnium oxide,zirconium oxide, titanium oxide, zinc oxide, indium oxide, tin oxide,indium tin oxide, tantalum oxide, silicon oxide, manganese oxide, nickeloxide, erbium oxide, cobalt oxide, tellurium oxide, barium titanate,titanium nitride, tantalum nitride, aluminum nitride, tungsten nitride,cobalt nitride, manganese nitride, hafnium nitride, ruthenium, platinum,nickel, cobalt, manganese, or copper can be used.

In the display device, a liquid crystal element can be included.

In the display device, an organic EL element can be included.

Furthermore, a structure where a display device, a microphone, and aspeaker are included can be employed.

One embodiment of the present invention is a method for manufacturing adisplay device including the steps of forming a transistor, a capacitor,a pixel electrode, and a first insulating layer over a first surface ofa first substrate, forming a light-blocking layer, a coloring layer, aninsulating layer, a spacer, and a second insulating layer over a firstsurface of a second substrate, bonding the first substrate and thesecond substrate with an adhesive layer to seal the transistor, thecapacitor, and liquid crystal, and providing a protective film incontact with the first substrate, the first insulating layer, theadhesive layer, the second insulating layer, and the second substrate inthe vicinity of a peripheral portion of the first substrate and thesecond substrate.

One embodiment of the present invention is a method for manufacturing adisplay device including the steps of forming a transistor, a capacitor,a pixel electrode, and a first insulating layer over a first surface ofa first substrate, forming a light-blocking layer, a coloring layer, aninsulating layer, a spacer, and a second insulating layer over a firstsurface of a second substrate, bonding the first substrate and thesecond substrate with an adhesive layer to seal the transistor, thecapacitor, and a display element, forming a groove portion by performinga first cutting treatment on the second substrate, forming a protectivefilm in contact with the first substrate, the first insulating layer,the adhesive layer, the second insulating layer, and the secondsubstrate in the vicinity of a peripheral portion of the groove portion,the first substrate, and the second substrate, and fabricating aplurality of display devices by performing a second cutting treatment onthe first substrate.

The protective film can be formed by an ALD method.

Furthermore, with an ALD method, the protective film can be formed usingaluminum oxide, hafnium oxide, zirconium oxide, titanium oxide, zincoxide, indium oxide, tin oxide, indium tin oxide, tantalum oxide,silicon oxide, manganese oxide, nickel oxide, erbium oxide, cobaltoxide, tellurium oxide, barium titanate, titanium nitride, tantalumnitride, aluminum nitride, tungsten nitride, cobalt nitride, manganesenitride, hafnium nitride, ruthenium, platinum, nickel, cobalt,manganese, or copper.

Note that other embodiments of the present invention are shown below inthe description of Embodiments and the drawings.

One embodiment of the present invention can provide a display device inwhich a peripheral circuit portion has high operation stability.

Another embodiment of the present invention can provide a display devicewith a narrow frame.

Another embodiment of the present invention can provide a lightweightdisplay device.

Another embodiment of the present invention can provide ahigh-definition display device.

Another embodiment of the present invention can provide a highlyreliable display device.

Another embodiment of the present invention can provide a large-areadisplay device.

Another embodiment of the present invention can provide a low-powerdisplay device.

Another embodiment of the present invention can provide a novel displaydevice or the like.

Alternatively, a method for manufacturing the display device can beprovided.

Note that the description of these effects does not disturb theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C are a top view and cross-sectional views illustrating adisplay device of one embodiment of the present invention;

FIGS. 2A and 2B are cross-sectional views each illustrating the displaydevice of one embodiment of the present invention;

FIGS. 3A to 3C are cross-sectional views illustrating a method formanufacturing a display device of one embodiment of the presentinvention;

FIGS. 4A to 4D are cross-sectional views illustrating a method formanufacturing a display device of one embodiment of the presentinvention;

FIGS. 5A to 5D are schematic cross-sectional views illustrating a filmformation principle;

FIGS. 6A and 6B are a schematic cross-sectional view of a depositionapparatus and a schematic top view of a manufacturing apparatusincluding one chamber corresponding to the deposition apparatus;

FIGS. 7A and 7B are schematic cross-sectional views of depositionapparatuses;

FIGS. 8A and 8B are a top view and a cross-sectional view illustrating adisplay device of one embodiment of the present invention;

FIG. 9 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 10 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 11 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 12 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 13 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 14 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 15 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIGS. 16A to 16D are top views illustrating an input device of oneembodiment of the present invention;

FIGS. 17A to 17D are top views illustrating an input device of oneembodiment of the present invention;

FIGS. 18A to 18C are top views illustrating an input device of oneembodiment of the present invention;

FIGS. 19A to 19F are top views illustrating an input device of oneembodiment of the present invention;

FIGS. 20A and 20B are circuit diagrams illustrating an input device ofone embodiment of the present invention;

FIGS. 21A and 21B are circuit diagrams illustrating an input device ofone embodiment of the present invention;

FIG. 22 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 23 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 24 is a cross-sectional view illustrating a display device of oneembodiment of the present invention;

FIG. 25 is a top view illustrating a display device of one embodiment ofthe present invention;

FIGS. 26A and 26B are cross-sectional views each illustrating atransistor of one embodiment of the present invention;

FIGS. 27A and 27B are cross-sectional views each illustrating atransistor of one embodiment of the present invention;

FIGS. 28A to 28C are a top view and cross-sectional views illustrating atransistor of one embodiment of the present invention;

FIGS. 29A to 29C are a top view and circuit diagrams illustrating adisplay device of one embodiment of the present invention;

FIGS. 30A to 30C are Cs-corrected high-resolution TEM images of a crosssection of a CAAC-OS and FIG. 30D is a schematic cross-sectional view ofa CAAC-OS;

FIGS. 31A to 31D are Cs-corrected high-resolution TEM images of a planeof a CAAC-OS;

FIGS. 32A to 32C show structural analysis of a CAAC-OS and a singlecrystal oxide semiconductor by XRD;

FIGS. 33A and 33B each show an electron diffraction pattern of aCAAC-OS;

FIG. 34 shows a change in crystal part of an In—Ga—Zn oxide induced byelectron irradiation;

FIGS. 35A and 35B are schematic views showing deposition models of aCAAC-OS and an nc-OS;

FIGS. 36A to 36C show an InGaZnO₄ crystal and a pellet;

FIGS. 37A to 37D are schematic views showing a deposition model of aCAAC-OS;

FIGS. 38A to 38F illustrate electronic devices of one embodiment of thepresent invention; and

FIGS. 39A to 39D illustrate electronic devices of one embodiment of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below. Note that in the structures of the inventiondescribed below, the same portions or portions having similar functionsare denoted by the same reference numerals in different drawings, anddescription of such portions is not repeated.

<Notes on the Description for Drawings>

In this specification, terms for describing arrangement, such as “over”and “under”, are used for convenience to describe a positionalrelationship between components with reference to drawings. Furthermore,the positional relationship between components is changed as appropriatein accordance with a direction in which each component is described.Thus, there is no limitation on terms used in this specification, anddescription can be made appropriately depending on the situation.

The term “over” or “below” does not necessarily mean that a component isplaced directly on or directly below and directly in contact withanother component. For example, the expression “electrode B overinsulating layer A” does not necessarily mean that the electrode B is onand in direct contact with the insulating layer A and can mean the casewhere another component is provided between the insulating layer A andthe electrode B.

In this specification, the term “parallel” indicates that the angleformed between two straight lines is greater than or equal to −10° andless than or equal to 10°, and accordingly also includes the case wherethe angle is greater than or equal to −5° and less than or equal to 5°.The term “substantially parallel” indicates that the angle formedbetween two straight lines is greater than or equal to −30° and lessthan or equal to 30°. The term “perpendicular” indicates that the angleformed between two straight lines is greater than or equal to 80° andless than or equal to 100°, and accordingly includes the case where theangle is greater than or equal to 85° and less than or equal to 95°. Theterm “substantially perpendicular” indicates that the angle formedbetween two straight lines is greater than or equal to 60° and less thanor equal to 120°.

In this specification, trigonal and rhombohedral crystal systems areincluded in a hexagonal crystal system.

In drawings, the size, the layer thickness, or the region is determinedarbitrarily for description convenience. Therefore, the size, the layerthickness, or the region is not limited to the illustrated scale. Notethat the drawings are schematically shown for clarity, and embodimentsof the present invention are not limited to shapes or values shown inthe drawings.

In drawings such as plan views (also referred to as layout views) andperspective views, some of components might not be illustrated forclarity of the drawings.

<Notes on Expressions that can be Rephrased>

In this specification and the like, in describing connections of atransistor, one of a source and a drain is referred to as “one of asource and a drain” (or a first electrode or a first terminal), and theother of the source and the drain is referred to as “the other of thesource and the drain” (or a second electrode or a second terminal). Thisis because a source and a drain of a transistor are interchangeabledepending on the structure, operation conditions, or the like of thetransistor. Note that the source or the drain of the transistor can alsobe referred to as a source (or drain) terminal, a source (or drain)electrode, or the like as appropriate depending on the situation.

In addition, in this specification and the like, the term such as an“electrode” or a “wiring” does not limit a function of the component.For example, an “electrode” is used as part of a “wiring” in some cases,and vice versa. Further, the term “electrode” or “wiring” can also meana combination of a plurality of “electrodes” and “wirings” formed in anintegrated manner.

In this specification and the like, a transistor is an element having atleast three terminals: a gate, a drain, and a source. The transistor hasa channel region between the drain (a drain terminal, a drain region, ora drain electrode) and the source (a source terminal, a source region,or a source electrode), and current can flow through the drain, thechannel region, and the source.

Since the source and the drain of the transistor change depending on thestructure, operating conditions, and the like of the transistor, it isdifficult to define which is a source or a drain. Thus, a portion thatfunctions as a source or a portion is not referred to as a source or adrain in some cases. In that case, one of the source and the drain mightbe referred to as a first electrode, and the other of the source and thedrain might be referred to as a second electrode.

In this specification, ordinal numbers such as first, second, and thirdare used to avoid confusion among components, and thus do not limit thenumber of the components.

In this specification and the like, a structure in which a flexibleprinted circuit (FPC), a tape carrier package (TCP), or the like isattached to a substrate of a display panel, or a structure in which anintegrated circuit (IC) is directly mounted on a substrate by a chip onglass (COG) method is referred to as a display device in some cases.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film” insome cases. In addition, the term “insulating film” can be changed intothe term “insulating layer” in some cases.

<Notes on Definitions of Terms>

The following are definitions of the terms that are not mentioned in theabove embodiments.

<<Connection>>

In this specification, when it is described that “A and B are connectedto each other”, the case where A and B are electrically connected toeach other is included in addition to the case where A and B aredirectly connected to each other. Here, the expression “A and B areelectrically connected” means the case where electric signals can betransmitted and received between A and B when an object having anyelectric action exists between A and B.

Note that these expressions are examples and there is no limitation onthe expressions. Here, X, Y, Z1, and Z2 each denote an object (e.g., adevice, an element, a circuit, a wiring, an electrode, a terminal, aconductive film, and a layer).

Note that a content (or may be part of the content) described in oneembodiment may be applied to, combined with, or replaced by a differentcontent (or may be part of the different content) described in theembodiment and/or a content (or may be part of the content) described inone or a plurality of different embodiments.

Note that in each embodiment, a content described in the embodiment is acontent described with reference to a variety of diagrams or a contentdescribed with a text described in this specification.

Note that by combining a diagram (or may be part of the diagram)illustrated in one embodiment with another part of the diagram, adifferent diagram (or may be part of the different diagram) illustratedin the embodiment, and/or a diagram (or may be part of the diagram)illustrated in one or a plurality of different embodiments, much morediagrams can be formed.

Embodiment 1

In this embodiment, structure examples of a display panel are described.

<<Protection of Substrate Surface Portion and Side Surface Portion byProtective Film>>

FIG. 1A is a top view of a display device. In FIG. 1A, a display device10 can be formed using a display region 21, a display panel 20 providedwith a peripheral circuit 22, and an FPC 42. In one embodiment of thepresent invention, a protective film 23 can be uniformly formed on thedisplay panel 20. The protective film 23 is preferably formed by anatomic layer deposition (ALD) method, for example. Note that aprotective film such as the protective film 23 has a function ofprotecting a display element and a transistor, for example. Theprotective film such as the protective film 23 may have anotherfunction, for example. Thus, the protective film such as the protectivefilm 23 may be simply referred to as a film. For example, the protectivefilm such as the protective film 23 may be referred to as a first film,a second film, or the like.

FIG. 1B is a cross-sectional view of an edge portion of the displaypanel 20. The display panel 20 is provided with a transistor, acapacitor, a display element, and the like, includes a substrate 100, asubstrate 300, an insulating layer 130, an insulating layer 131, aninsulating layer 170, an insulating layer 180, a light-blocking layer18, an insulating layer 330, and a spacer 240 in the edge portion, andis covered with the protective film 23.

<<Deposition Method of Protective Film on Display Panel by ALD Method>>

FIGS. 3A to 3C illustrate a deposition method of a protective film onthe display panel 20 by an ALD method.

Part of the transistor, the capacitor, and the display element and thelike are formed over the substrate 100, so that a region 11 is formed.In addition, the light-blocking layer 18, the insulating layer 330, partof a coloring layer and a display element, and the like are formed overthe substrate 300, so that a region 12 is formed (see FIG. 3A).

Next, the region 11 of the substrate 100 and the region 12 of thesubstrate 300 are made to face each other, and the substrate 100 and thesubstrate 300 are bonded to each other with an adhesive layer 370, sothat the display panel 20 can be fabricated (see FIG. 3B).

Then, the protective film 23 can be deposited on the display panel 20 byan ALD method (see FIG. 3C). Note that a portion to which the FPC 42 isconnected is masked to prevent the protective film 23 from beingdeposited on the portion.

By an ALD method, the protective film can be deposited extremelyuniformly on a surface on which the protective film is deposited. Byusing an ALD method, for example, aluminum oxide, hafnium oxide,zirconium oxide, titanium oxide, zinc oxide, indium oxide, tin oxide,indium tin oxide (ITO), tantalum oxide, silicon oxide, manganese oxide,nickel oxide, erbium oxide, cobalt oxide, tellurium oxide, bariumtitanate, titanium nitride, tantalum nitride, aluminum nitride, tungstennitride, cobalt nitride, manganese nitride, hafnium nitride, and thelike can be deposited as the protective film. Furthermore, theprotective film is not limited to an insulating film, and a conductivefilm may also be deposited. For example, ruthenium, platinum, nickel,cobalt, manganese, copper, and the like can be deposited.

Furthermore, a portion electrically connected to the FPC 42 or the likeis preferably masked so that the protective film is not deposited on theportion. For the masking, an organic film, an inorganic film, a metal,or the like can be used. For example, an oxide insulating film such assilicon oxide, silicon oxynitride, gallium oxide, gallium oxynitride,yttrium oxide, yttrium oxynitride, hafnium oxide, or hafnium oxynitride,a nitride insulating film such as silicon nitride or aluminum nitride,or an organic material such as a photoresist, a polyimide resin, anacrylic resin, a polyimide amide resin, a benzocyclobutene resin, apolyamide resin, or an epoxy resin can be used. In the case where any ofthese films is used as a mask, the mask is preferably removed after theprotective film is deposited.

Furthermore, a region on which the protective film is deposited can bemasked with a metal mask by an ALD method. The metal mask can be formedusing a metal element selected from iron, chromium, nickel, cobalt,tungsten, molybdenum, aluminum, copper, tantalum, and titanium, an alloyincluding any of the metal elements, an alloy including any of the metalelements in combination, or the like. The metal mask can be positionedin the proximity of or in contact with the display panel.

A film formed by an ALD method is extremely uniform and dense. When theprotective film 23 is deposited on the side surface portion of thedisplay panel by an ALD method, entry of external components such asmoisture can be inhibited. As a result, a change in transistorcharacteristics can be inhibited and the operation of the peripheralcircuit can be stable. Moreover, the frame size can be reduced, thepixel region can be enlarged, and the definition of the display devicecan be increased.

With the protective film 23, even if a distance A-A3 between an edgeportion of the peripheral circuit 22 and the edge portion of the displaypanel 20 is narrowed, the stable transistor characteristics areobtained, that is, the peripheral circuit operates stably because of ahigh barrier property of the protective film 23; thus, the frame of thedisplay panel can be narrowed. For example, the distance between theperipheral circuit 22 and the edge portion of the display panel 20 (acut portion when the panel is processed) can be 300 μm or shorter,preferably 200 μm or shorter. Alternatively, the edge portion of thedisplay panel 20 may have a structure without unevenness as illustratedin FIG. 1C.

<<Another Structure Example of Formation of Protective Film>>

FIGS. 2A and 2B show other examples of FIG. 1B. A region on which theprotective film 23 is to be deposited can be controlled by masking. Inthis case, the protective film 23 can be slightly deposited on rearsurface sides (regions 13) as illustrated in FIG. 2A, or the depositionof the protective film 23 on a rear surface side (a region 14) can beprevented as illustrated in FIG. 2B.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 2

In this embodiment, a method for manufacturing the plurality of displaypanels described in Embodiment 1 is described.

FIGS. 4A to 4D illustrate a manufacturing method of the display panel20. In FIGS. 4A to 4D, a liquid crystal element 80 and the adhesivelayer 370 are illustrated as a display element, and a display panel canbe formed by bonding an element substrate where a pixel, a transistor, acapacitor, and the like are provided for the substrate 100 and a countersubstrate where a light-blocking layer, a coloring layer, and the likeare provided for the substrate 300 to seal liquid crystal. Note thatportions similar to those of the manufacturing method in FIGS. 3A to 3Care omitted.

In a structure including the plurality of display panels 20 (FIG. 4A),the substrate 300 (an upper side) is cut to form a groove portion 30(FIG. 4B). After the formation of the groove portion 30, the protectivefilm 23 is formed from the upper side by an ALD method (FIG. 4C), andthe substrate 100 is cut, whereby the plurality of display panels can befinally manufactured (FIG. 4D). Note that in this case, the formation ofthe protective film 23 on a rear surface of the substrate 100 (a surfaceon which the liquid crystal element 80 is not provided) can beinhibited.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 3

<<Deposition Method>>

A deposition apparatus which can be used for forming a semiconductorlayer, an insulating layer, a conductive layer, and the like, which canbe used in one embodiment of the present invention, is described below.

<<CVD and ALD>>

In a conventional deposition apparatus utilizing a CVD method, sourcegases (precursors) for reaction are supplied to a chamber at the sametime at the time of deposition. In a deposition apparatus utilizing anALD method, precursors for reaction are sequentially introduced into achamber, and then the sequence of the gas introduction is repeated. Forexample, two or more kinds of precursors are sequentially supplied tothe chamber by switching respective switching valves (also referred toas high-speed valves). For example, a first precursor is introduced, aninert gas (e.g., argon or nitrogen) or the like is introduced after theintroduction of the first precursor so that the plural kinds ofprecursors are not mixed, and then a second precursor is introduced.Alternatively, the first precursor may be exhausted by vacuum evacuationinstead of the introduction of the inert gas, and then the secondprecursor may be introduced. FIGS. 5A to 5D illustrate a depositionprocess of an ALD method. A first precursor 601 is adsorbed to thesurface of the substrate (see FIG. 5A), a first single layer isdeposited (see FIG. 5B), the first single layer reacts with a secondprecursor 602 to be introduced later (see FIG. 5C), and a second singlelayer is stacked over the first single layer to form a thin film (seeFIG. 5D). The sequence of the gas introduction is repeated plural timesuntil a desired thickness is obtained, whereby a thin film withexcellent step coverage can be formed. The thickness of the thin filmcan be adjusted by the number of repetition times of the sequence of thegas introduction; therefore, an ALD method makes it possible toaccurately adjust a thickness.

An ALD method includes an ALD method using heating (thermal ALD method)and an ALD method using plasma (plasma ALD method). In the thermal ALDmethod, precursors react with each other using thermal energy, and inthe plasma ALD method, precursors react with each other in a state of aradical.

With an ALD method, an extremely thin film can be formed with highaccuracy. In addition, the coverage of an uneven surface with the filmand the film density of the film are high.

Furthermore, plasma damage is not caused when the thermal ALD method isemployed.

<<Plasma ALD>>

Alternatively, when the plasma ALD method is employed, the film can beformed at a lower temperature than when the thermal ALD method isemployed. With the plasma ALD method, for example, the film can beformed without decreasing the deposition rate even at 100° C. or lower.Moreover, in the plasma ALD method, nitrogen radicals can be formed byplasma; thus, a nitride film as well as an oxide film can be formed.

Furthermore, in the case where a light-emitting element (such as anorganic EL element) is used as a display element, when a processtemperature is high, the deterioration of the light-emitting element maybe accelerated. Here, with the plasma ALD method, the processtemperature can be lowered; thus, the deterioration of thelight-emitting element can be inhibited.

In addition, in the case of using the plasma ALD, inductively coupledplasma (ICP) is used to generate radical species. Accordingly, plasmacan be generated at a place apart from the substrate, so that plasmadamage can be inhibited.

As described above, with the plasma ALD method, the process temperaturecan be lowered and the coverage of the surface can be increased ascompared with other deposition methods, and the protective film can bedeposited on the side surface portion of the substrate after the displaypanel is fabricated. Thus, entry of water from the outside can beinhibited. Therefore, the reliability of driver operation of aperipheral circuit at an edge portion of a panel is improved (thetransistor characteristics are improved), so that a stable operation canbe achieved even in the case of employing a narrow frame.

<<ALD Apparatus>>

FIG. 6A illustrates an example of a deposition apparatus utilizing anALD method. The deposition apparatus utilizing an ALD method includes adeposition chamber (chamber 1701), source material supply portions 1711a and 1711 b, high-speed valves 1712 a and 1712 b which are flow ratecontrollers, source material introduction ports 1713 a and 1713 b, asource material exhaust port 1714, and an evacuation unit 1715. Thesource material introduction ports 1713 a and 1713 b provided in thechamber 1701 are connected to the source material supply portions 1711 aand 1711 b, respectively, through supply tubes and valves. The sourcematerial exhaust port 1714 is connected to the evacuation unit 1715through an exhaust tube, a valve, and a pressure controller.

A substrate holder 1716 with a heater is provided in the chamber, and asubstrate 1700 over which a film is formed is provided over thesubstrate holder.

In the source material supply portions 1711 a and 1711 b, a precursor isformed from a solid source material or a liquid source material by usinga vaporizer, a heating unit, or the like. Alternatively, the sourcematerial supply portions 1711 a and 1711 b may supply a precursor.

Although two source material supply portions 1711 a and 1711 b areprovided as an example, without limitation thereto, three or more sourcematerial supply portions may be provided. The high-speed valves 1712 aand 1712 b can be accurately controlled by time, and a precursor and aninert gas are supplied by the high-speed valves 1712 a and 1712 b. Thehigh-speed valves 1712 a and 1712 b are flow rate controllers for aprecursor, and can also be referred to as flow rate controllers for aninert gas.

In the deposition apparatus illustrated in FIG. 6A, a thin film isformed over a surface of the substrate 1700 in the following manner: thesubstrate 1700 is transferred to put on the substrate holder 1716, thechamber 1701 is sealed, the substrate 1700 is heated to a desiredtemperature (e.g., higher than or equal to 100° C. or higher than orequal to 150° C.) by heating the substrate holder 1716 with a heater;and supply of a precursor, evacuation with the evacuation unit 1715,supply of an inert gas, and evacuation with the evacuation unit 1715 arerepeated.

In the deposition apparatus illustrated in FIG. 6A, an insulating layerformed using an oxide (including a composite oxide) containing one ormore elements selected from hafnium, aluminum, tantalum, zirconium, andthe like can be formed by selecting a source material (e.g., a volatileorganometallic compound) used for the source material supply portions1711 a and 1711 b appropriately. Specifically, it is possible to use aninsulating layer formed using hafnium oxide, an insulating layer formedusing aluminum oxide, an insulating layer formed using hafnium silicate,or an insulating layer formed using aluminum silicate. Alternatively, athin film, e.g., a metal layer such as a tungsten layer or a titaniumlayer, or a nitride layer such as a titanium nitride layer can be formedby selecting a source material (e.g., a volatile organometalliccompound) used for the source material supply portions 1711 a and 1711 bappropriately.

For example, in the case where a hafnium oxide layer is formed by adeposition apparatus using an ALD method, two kinds of gases, i.e.,ozone (O₃) as an oxidizer and a precursor which is obtained byvaporizing liquid containing a solvent and a hafnium precursor compound(hafnium alkoxide or hafnium amide such astetrakis(dimethylamide)hafnium (TDMAH)) are used. In this case, thefirst precursor supplied from the source material supply portion 1711 ais TDMAH, and the second precursor supplied from the source materialsupply portion 1711 b is ozone. Note that the chemical formula oftetrakis(dimethylamide)hafnium is Hf[N(CH₃)₂]₄. Examples of anothermaterial include tetrakis(ethylmethylamide)hafnium. Note that nitrogenhas a function of eliminating charge trap states. Therefore, when theprecursor contains nitrogen, a hafnium oxide film having low density ofcharge trap states can be formed.

For example, in the case where an aluminum oxide layer is formed by adeposition apparatus utilizing an ALD method, two kinds of gases, e.g.,H₂O as an oxidizer and a precursor which is obtained by vaporizingliquid containing a solvent and an aluminum precursor compound (e.g.,trimethylaluminum (TMA)) are used. In this case, the first precursorsupplied from the source material supply portion 1711 a is TMA, and thesecond precursor supplied from the source material supply portion 1711 bis H₂O. Note that the chemical formula of trimethylaluminum is Al(CH₃)₃.Examples of another material liquid include tris(dimethylamide)aluminum,triisobutylaluminum, and aluminumtris(2,2,6,6-tetramethyl-3,5-heptanedionate).

<<Multi-Chamber Manufacturing Apparatus>>

FIG. 6B illustrates an example of a multi-chamber manufacturingapparatus including at least one deposition apparatus illustrated inFIG. 6A.

In the manufacturing apparatus illustrated in FIG. 6B, a stack of filmscan be successively formed without exposure to the air, and entry ofimpurities is prevented and throughput is improved.

The manufacturing apparatus illustrated in FIG. 6B includes at least aload chamber 1702, a transfer chamber 1720, a pretreatment chamber 1703,a chamber 1701 which is a deposition chamber, and an unload chamber1706. Note that in order to prevent attachment of moisture, the chambersof the manufacturing apparatus (including the load chamber, thetreatment chamber, the transfer chamber, the deposition chamber, theunload chamber, and the like) are preferably filled with an inert gas(such as a nitrogen gas) whose dew point is controlled, more preferablymaintain reduced pressure.

The chambers 1704 and 1705 may be deposition apparatuses utilizing anALD method like the chamber 1701, deposition apparatuses utilizing aplasma CVD method, deposition apparatuses utilizing a sputtering method,or deposition apparatuses utilizing a metal organic chemical vapordeposition (MOCVD) method.

For example, an example in which a stack of films is formed under acondition that the chamber 1704 is a deposition apparatus utilizing aplasma CVD method and the chamber 1705 is a deposition apparatusutilizing an MOCVD method is shown below.

Although FIG. 6B shows an example in which a top view of the transferchamber 1720 is a hexagon, a manufacturing apparatus in which the topsurface shape is set to a polygon having more than six corners and morechambers are connected depending on the number of layers of a stack maybe used. The top surface shape of the substrate is rectangular in FIG.6B; however, there is no particular limitation on the top surface shapeof the substrate. Although FIG. 6B shows an example of the single wafertype, a batch-type deposition apparatus in which a plurality ofsubstrates are formed at a time may be used.

<<Large Area ALD Apparatus>>

Moreover, with the plasma ALD method, a film can be deposited on a largesubstrate. FIGS. 7A and 7B are schematic views of other examples of theALD apparatus. A gas which is made into plasma (precursor) is introducedfrom an introduction port 810 into a chamber 820, and a film can bedeposited on a substrate 800 from above and below by an ALD method. Asfor the deposition method, the film can be deposited with the substratefixed in the chamber as illustrated in FIG. 7A, or the film can bedeposited while the substrate is carried by an in-line method asillustrated in FIG. 7B. By using the plasma ALD method, the film can bedeposited with high throughput and in a large area.

Embodiment 4

In this embodiment, the details of the display device described inEmbodiments 1 and 2 are described with reference to drawings.

FIGS. 8A and 8B are examples of a top view and a cross-sectional view ofthe display device. Note that FIG. 8A illustrates a typical structureincluding the display panel 20, the display region 21, the peripheralcircuit 22, and the FPC 42.

FIG. 8B is a cross-sectional view taken along dashed-dotted lines A-A′,B-B′, C-C′, and D-D′ in FIG. 8A.

<<Liquid Crystal Panel>>

As illustrated in FIG. 8B, a liquid crystal panel can be used as adisplay panel included in the display device. A display deviceillustrated in FIG. 8B includes a liquid crystal element 80 as a displayelement. The display device also includes a polarizing plate 103, apolarizing plate 303, and a backlight 104, which are bonded withadhesive layers 373, 374, and 375. Furthermore, a protective substrate302 is provided on the side closer to a viewer than the polarizing plate303 is, and is bonded with an adhesive layer 376.

<<Substrate 100>>

There is no particular limitation on a material and the like of asubstrate 100 as long as the material has heat resistance high enough towithstand at least heat treatment performed later. The materialdesirably has a high light-transmitting property.

For the substrate 100, an organic material, an inorganic material, acomposite material of an organic material and an inorganic material, orthe like can be used. For example, an inorganic material such as glass,a ceramic, or a metal can be used for the substrate 100.

Specifically, non-alkali glass, soda-lime glass, potash glass, crystalglass, or the like can be used for the substrate 100. Specifically, aninorganic oxide film, an inorganic nitride film, an inorganic oxynitridefilm, or the like can also be used for the substrate 100. Silicon oxide,silicon nitride, silicon oxynitride, alumina, stainless steel, aluminum,or the like can be used for the substrate 100.

A single-layer material or a stacked-layer material in which a pluralityof layers are stacked can be used for the substrate 100. For example, astacked-layer material in which a base, an insulating film that preventsdiffusion of impurities contained in the base, and the like are stackedcan be used for the substrate 100. Specifically, a stacked-layermaterial in which glass and one or a plurality of films that preventdiffusion of impurities contained in the glass and that are selectedfrom a silicon oxide layer, a silicon nitride layer, a siliconoxynitride layer, and the like are stacked can be used for the substrate100. Alternatively, a stacked-layer material in which a resin and a filmfor preventing diffusion of impurities that penetrate the resin, such asa silicon oxide film, a silicon nitride film, and a silicon oxynitridefilm are stacked can be used for the substrate 100.

The above-described substrate that can be used as the substrate 100 canbe used as the substrate 300 as well.

<<Transistors 50, 52>>

The transistor 50 can be formed using a conductive layer 120, insulatinglayers 130 and 131, a semiconductor layer 140, a conductive layer 150, aconductive layer 160, an insulating layer 170, and an insulating layer180. A transistor 52 can include similar components.

<<Insulating Layer 110>>

The insulating layer 110 that functions as a base film is formed usingsilicon oxide, silicon oxynitride, silicon nitride, silicon nitrideoxide, gallium oxide, hafnium oxide, yttrium oxide, aluminum oxide,aluminum oxynitride, or the like. Note that when silicon nitride,gallium oxide, hafnium oxide, yttrium oxide, aluminum oxide, or the likeis used as a material for the insulating layer 110, it is possible tosuppress diffusion of impurities such as alkali metal, water, andhydrogen into the semiconductor layer 140 from the substrate 100. Theinsulating layer 110 is formed over the substrate 100. The insulatinglayer 110 is not necessarily provided.

<<Conductive Layer 120>>

The conductive layer 120 that functions as a gate electrode is formedusing a metal element selected from aluminum, chromium, copper,tantalum, titanium, molybdenum, nickel, iron, cobalt, and tungsten; analloy containing any of these metal elements as a component; an alloycontaining any of these metal elements in combination; or the like.Furthermore, one or more metal elements selected from manganese andzirconium may be used. The conductive layer 120 may have a single-layerstructure or a layered structure of two or more layers. For example, anyof the following can be used: a single-layer structure of an aluminumfilm containing silicon; a single-layer structure of a copper filmcontaining manganese; a two-layer structure in which a titanium film isstacked over an aluminum film; a two-layer structure in which a titaniumfilm is stacked over a titanium nitride film; a two-layer structure inwhich a tungsten film is stacked over a titanium nitride film; atwo-layer structure in which a tungsten film is stacked over a tantalumnitride film or a tungsten nitride film; a two-layer structure in whicha copper film is stacked over a copper film containing manganese; athree-layer structure in which a titanium film, an aluminum film, and atitanium film are stacked in this order; a three-layer structure inwhich a copper film containing manganese, a copper film, and a copperfilm containing manganese are stacked in this order; and the like.Alternatively, an alloy film or a nitride film which contains aluminumand one or more elements selected from titanium, tantalum, tungsten,molybdenum, chromium, neodymium, and scandium may be used.

<<Insulating Layer 130>>

The insulating layer 130 functions as a gate insulating film. Theinsulating layer 130 can be formed using, for example, an insulatingfilm containing at least one of aluminum oxide, magnesium oxide, siliconoxide, silicon oxynitride, silicon nitride oxide, silicon nitride,gallium oxide, germanium oxide, yttrium oxide, zirconium oxide,lanthanum oxide, neodymium oxide, hafnium oxide, and tantalum oxide. Theinsulating layer 130 may be a stack of any of the above materials. Theinsulating layer 130 may contain lanthanum (La), nitrogen, or zirconium(Zr) as an impurity.

<<Insulating Layer 131>>

Furthermore, the gate insulating film can be a stack of the insulatinglayer 130 and the insulating layer 131. The insulating layer 131 can beformed using, for example, an insulating film containing at least one ofaluminum oxide, magnesium oxide, silicon oxide, silicon oxynitride,silicon nitride oxide, silicon nitride, gallium oxide, germanium oxide,yttrium oxide, zirconium oxide, lanthanum oxide, neodymium oxide,hafnium oxide, and tantalum oxide. The insulating layer 131 may be astack of any of the above materials. The insulating layer 131 maycontain lanthanum (La), nitrogen, zirconium (Zr), or the like as animpurity. With the insulating layer 131, it is possible to prevent entryof hydrogen, water, or the like into the semiconductor layer 140 fromthe outside.

<<Semiconductor Layer 140>>

The semiconductor layer 140 is formed using a metal oxide containing atleast In or Zn. The area of a top surface of the semiconductor layer 140is preferably the same as or smaller than the area of a top surface ofthe conductive layer 120.

<<Oxide Semiconductor>>

As an oxide semiconductor used for the aforementioned semiconductorlayer 140, any of the following can be used, for example: anIn—Ga—Zn-based oxide, an In—Al—Zn-based oxide, an In—Sn—Zn-based oxide,an In—Hf—Zn-based oxide, an In—La—Zn-based oxide, an In—Ce—Zn-basedoxide, an In—Pr—Zn-based oxide, an In—Nd—Zn-based oxide, anIn—Sm—Zn-based oxide, an In—Eu—Zn-based oxide, an In—Gd—Zn-based oxide,an In—Tb—Zn-based oxide, an In—Dy—Zn-based oxide, an In—Ho—Zn-basedoxide, an In—Er—Zn-based oxide, an In—Tm—Zn-based oxide, anIn—Yb—Zn-based oxide, an In—Lu—Zn-based oxide, an In—Sn—Ga—Zn-basedoxide, an In—Hf—Ga—Zn-based oxide, an In—Al—Ga—Zn-based oxide, anIn—Sn—Al—Zn-based oxide, an In—Sn—Hf—Zn-based oxide, anIn—Hf—Al—Zn-based oxide, and an In—Ga-based oxide.

Note that here, an “In—Ga—Zn-based oxide” means an oxide containing In,Ga, and Zn as its main components and there is no limitation on theratio of In:Ga:Zn. The In—Ga—Zn-based oxide may contain another metalelement in addition to In, Ga, and Zn.

When the semiconductor layer 140 is formed using an In-M-Zn oxide, theatomic ratio of In to M when the summation of In and M is assumed to be100 atomic % is preferably as follows: the proportion of In is higherthan 25 atomic % and the proportion of M is lower than 75 atomic %;further preferably, the proportion of In is higher than 34 atomic % andthe proportion of M is lower than 66 atomic %.

The energy gap of the semiconductor layer 140 is 2 eV or more,preferably 2.5 eV or more, and further preferably 3 eV or more. With theuse of an oxide semiconductor having such a wide energy gap, theoff-state current of the transistor 50 can be reduced.

The thickness of the semiconductor layer 140 desirably ranges from 3 nmto 200 nm, preferably from 3 nm to 100 nm, and further preferably from 3nm to 50 nm.

In the case where the semiconductor layer 140 is formed using an In-M-Znoxide (M is Al, Ga, Y, Zr, La, Ce, or Nd), it is preferable that theatomic ratio of metal elements of a sputtering target used for formingthe In-M-Zn oxide satisfy In M and Zn M. As the atomic ratio of metalelements of such a sputtering target, InM:Zn=1:1:1, InM:Zn=1:1:1.2,InM:Zn=3:1:2, and InM:Zn=4:2:4.1 are preferable. Note that the atomicratio of metal elements in the formed semiconductor layer 140 variesfrom the above atomic ratio of metal elements of the sputtering targetwithin a range of ±40% as an error. Note that a c-axis alignedcrystalline oxide semiconductor (CAAC-OS) film and a microcrystallineoxide semiconductor film that are described later can be formed using atarget including an In—Ga—Zn oxide, preferably a polycrystalline targetincluding an In—Ga—Zn oxide.

Hydrogen contained in the semiconductor layer 140 reacts with oxygenbonded to a metal atom to be water, and also causes oxygen vacancies ina lattice from which oxygen is released (or a portion from which oxygenis released). Due to entry of hydrogen into the oxygen vacancies, anelectron serving as a carrier is generated. Further, in some cases,bonding of part of hydrogen to oxygen bonded to a metal atom causesgeneration of an electron serving as a carrier. Thus, a transistorincluding an oxide semiconductor which contains hydrogen is likely to benormally on.

Accordingly, it is preferable that hydrogen as well as the oxygenvacancies in the semiconductor layer 140 be reduced as much as possible.Specifically, in the semiconductor layer 140, the concentration ofhydrogen which is measured by secondary ion mass spectrometry (SIMS) isset to lower than or equal to 5×10¹⁹ atoms/cm³, preferably lower than orequal to 1×10¹⁹ atoms/cm³, further preferably lower than or equal to5×10¹⁸ atoms/cm³, still further preferably lower than or equal to 1×10¹⁸atoms/cm³, yet still further preferably lower than or equal to 5×10¹⁷atoms/cm³, and still more preferably lower than or equal to 1×10¹⁶atoms/cm³. As a result, the transistor 50 has a positive thresholdvoltage (also referred to as normally-off characteristics).

When silicon or carbon which is one of the elements belonging to Group14 is contained in the semiconductor layer 140, oxygen vacancies areincreased in the semiconductor layer 140, and the semiconductor layer140 has n-type conductivity. Thus, the concentration of silicon orcarbon (the concentration is measured by SIMS) in the semiconductorlayer 140 is lower than or equal to 2×10¹⁸ atoms/cm³, preferably lowerthan or equal to 2×10¹⁷ atoms/cm³. As a result, the transistor 50 has apositive threshold voltage (also referred to as normally-offcharacteristics).

Furthermore, the concentration of alkali metal or alkaline earth metalin the semiconductor layer 140, which is measured by SIMS, is lower thanor equal to 1×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁶atoms/cm³. Alkali metal and alkaline earth metal might generate carrierswhen bonded to an oxide semiconductor, in which case the off-statecurrent of the transistor might be increased. Therefore, it ispreferable to reduce the concentration of alkali metal or alkaline earthmetal in the semiconductor layer 140. As a result, the transistor 50 hasa positive threshold voltage (also referred to as normally-offcharacteristics).

Furthermore, when nitrogen is contained in the semiconductor layer 140,electrons serving as carriers are generated to increase the carrierdensity, so that the semiconductor layer 140 easily has n-typeconductivity. Thus, the transistor tends to have normally-oncharacteristics. For this reason, nitrogen in the semiconductor layer140 is preferably reduced as much as possible; for example, theconcentration of nitrogen which is measured by SIMS is preferably set tolower than or equal to 5×10¹⁸ atoms/cm³.

When impurities in the semiconductor layer 140 are reduced, the carrierdensity of the semiconductor layer 140 can be lowered. The carrierdensity of the semiconductor layer 140 is 1×10¹⁵/cm³ or less, preferably1×10¹³/cm³ or less, further preferably 8×10¹¹/cm³ or less, furtherpreferably less than 1×10¹¹/cm³, further preferably less than1×10¹⁰/cm³, and 1×10⁻⁹/cm³ or more.

When an oxide semiconductor having a low impurity concentration and alow density of defect states is used for the semiconductor layer 140,the transistor can have more excellent electrical characteristics. Here,the state in which impurity concentration is low and the density ofdefect states is low (the amount of oxygen vacancies is small) isreferred to as “highly purified intrinsic” or “substantially highlypurified intrinsic.” A highly purified intrinsic or substantially highlypurified intrinsic oxide semiconductor has few carrier generationsources, and thus has a low carrier density in some cases. Thus, thetransistor whose channel region is formed in the semiconductor layer 140including the oxide semiconductor is likely to have a positive thresholdvoltage (also referred to as normally-off characteristics). A highlypurified intrinsic or substantially highly purified intrinsic oxidesemiconductor has a low density of defect states and accordingly has alow density of trap states in some cases. The transistor including thesemiconductor layer 140 containing the highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor has anextremely low off-state current; the off-state current can be less thanor equal to the measurement limit of a semiconductor parameter analyzer,i.e., less than or equal to 1×10⁻¹³ A, at a voltage (drain voltage)between a source electrode and a drain electrode of from 1 V to 10 V. Inaddition, variation in characteristics can be prevented.

In the case where the voltage between a source and a drain is set toabout 0.1 V, 5 V, or 10 V, for example, the off-state currentstandardized on the channel width of the transistor 50 in which thesemiconductor layer 140 is used for the semiconductor layer can be aslow as several yoctoamperes per micrometer to several zeptoamperes permicrometer.

When a transistor with an extremely low off-state leakage current isused as the transistor 50 connected to a display element (e.g., a liquidcrystal element 80), the time for holding image signals can be extended.For example, images can be held even when the frequency of writing imagesignals is higher than or equal to 11.6 μHz (once a day) and less than0.1 Hz (0.1 times a second), preferably higher than or equal to 0.28 mHz(once an hour) and less than 1 Hz (once a second). As a result, thefrequency of writing image signals can be reduced, leading to areduction in the power consumption of the display panel 20. Needless tosay, the frequency of writing image signals can be higher than or equalto 1 Hz, preferably higher than or equal to 30 Hz (30 times a second),further preferably higher than or equal to 60 Hz (60 times a second) andless than 960 Hz (960 times a second).

From the above reason, the use of a transistor containing an oxidesemiconductor allows fabrication of a highly reliable display panel withlow power consumption.

In the transistor containing an oxide semiconductor, the semiconductorlayer 140 can be formed by a sputtering method, an MOCVD method, apulsed laser deposition (PLD) method, or the like. When a sputteringmethod is used, the transistor can be used in a large-area displaydevice.

Note that instead of the semiconductor layer 140, a semiconductor layerincluding silicon or silicon germanium may be used. The semiconductorlayer including silicon or silicon germanium can have an amorphousstructure, a polycrystalline structure, or a single crystal structure,as appropriate.

<<Insulating Layer 170>>

The insulating layer 170 has a function of protecting the channel regionof the transistor. The insulating layer 170 is formed using an oxideinsulating film such as silicon oxide, silicon oxynitride, aluminumoxide, aluminum oxynitride, gallium oxide, gallium oxynitride, yttriumoxide, yttrium oxynitride, hafnium oxide, or hafnium oxynitride, or anitride insulating film such as silicon nitride or aluminum nitride. Theinsulating layer 170 can have a single-layer structure or astacked-layer structure.

The insulating layer 170 is preferably formed using an oxide insulatingfilm containing more oxygen than that in the stoichiometric composition.Part of oxygen is released by heating from the oxide insulating filmcontaining more oxygen than that in the stoichiometric composition. Theoxide insulating film containing more oxygen than that in thestoichiometric composition is an oxide insulating film of which theamount of released oxygen atoms is greater than or equal to 1.0×10¹⁸atoms/cm³, preferably greater than or equal to 3.0×10²⁰ atoms/cm³ inthermal desorption spectroscopy (TDS) analysis in which heat treatmentis performed such that a temperature of a film surface is higher than orequal to 100° C. and lower than or equal to 700° C. or higher than orequal to 100° C. and lower than or equal to 500° C. By the heattreatment, oxygen contained in the insulating layer 170 can betransferred to the semiconductor layer 140, so that the amount of oxygenvacancies in the semiconductor layer 140 can be reduced.

<<Insulating Layer 180>>

When an insulating film having a blocking effect against oxygen,hydrogen, water, and the like is provided as the insulating layer 180,it is possible to prevent outward diffusion of oxygen from thesemiconductor layer 140 and entry of hydrogen, water, or the like intothe semiconductor layer 140 from the outside. The insulating layer 180can be formed using, for example, an insulating film containing at leastone of aluminum oxide, magnesium oxide, silicon oxide, siliconoxynitride, silicon nitride oxide, silicon nitride, gallium oxide,germanium oxide, yttrium oxide, zirconium oxide, lanthanum oxide,neodymium oxide, hafnium oxide, and tantalum oxide. The insulating layer180 may be a stack of any of the above materials. The insulating layer180 may contain lanthanum (La), nitrogen, or zirconium (Zr) as animpurity.

<<Capacitor 61, 63>>

A capacitor 61 includes the conductive layer 400, the insulating layer180, and the conductive layer 190. The conductive layer 400 functions asone electrode of the capacitor 61. The conductive layer 190 functions asthe other electrode of the capacitor 61. The insulating layer 180 isprovided between the conductive layer 400 and the conductive layer 190.A capacitor 63 can have a structure similar to that of the capacitor 61.

<<Conductive Layer 400>>

When the transistor 50 includes an oxide semiconductor in thesemiconductor layer 140, the conductive layer 400 can be formed of thesame material as the semiconductor layer 140 over the insulating layer130. In that case, the conductive layer 400 is formed by processing afilm formed at the same time as the semiconductor layer 140, andtherefore contains elements similar to those in the semiconductor layer140. The conductive layer 400 has a crystal structure similar to ordifferent from that of the semiconductor layer 140. When the film formedat the same time as the semiconductor layer 140 includes impurities oroxygen vacancies, the film can have conductivity to be the conductivelayer 400. Typical examples of the impurities contained in theconductive layer 400 are a rare gas, hydrogen, boron, nitrogen,fluorine, aluminum, and phosphorus. Typical examples of the rare gasinclude helium, neon, argon, krypton, and xenon. Note that theconductive layer 400 has conductivity as an example; however, oneembodiment of the present invention is not limited to this example andthe conductive layer 400 does not need to have conductivity depending onthe case or circumstances. In other words, the conductive layer 400 mayhave properties similar to those of the semiconductor layer 140.

Although the semiconductor layer 140 and the conductive layer 400 areformed over the insulating layer 130 as described above, they havedifferent impurity concentrations. Specifically, the impurityconcentration of the conductive layer 400 is higher than that of thesemiconductor layer 140. For example, in the semiconductor layer 140,the hydrogen concentration measured by secondary ion mass spectrometryis lower than or equal to 5×10¹⁹ atoms/cm³, preferably lower than orequal to 5×10¹⁸ atoms/cm³, further preferably lower than or equal to1×10¹⁸ atoms/cm³, still further preferably lower than or equal to 5×10¹⁷atoms/cm³, and yet still further preferably lower than or equal to1×10¹⁶ atoms/cm³. In contrast, the hydrogen concentration in theconductive layer 400 measured by secondary ion mass spectrometry ishigher than or equal to 8×10¹⁹ atoms/cm³, preferably higher than orequal to 1×10²⁰ atoms/cm³, and further preferably higher than or equalto 5×10²⁰ atoms/cm³. In addition, the hydrogen concentration in theconductive layer 400 is greater than or equal to 2 times or greater thanor equal to 10 times that in the semiconductor layer 140.

When the hydrogen concentration in the semiconductor layer 140 is set inthe aforementioned range, generation of electrons serving as carriers inthe semiconductor layer 140 can be suppressed.

When an oxide semiconductor film formed at the same time as thesemiconductor layer 140 is exposed to plasma, the oxide semiconductorfilm is damaged and oxygen vacancies can be generated. For example, whena film is formed over the oxide semiconductor film by a plasma CVDmethod or a sputtering method, the oxide semiconductor film is exposedto plasma and oxygen vacancies are generated. Alternatively, when theoxide semiconductor film is exposed to plasma in etching treatment forformation of an opening in the insulating layer 170, oxygen vacanciesare generated. Alternatively, when the oxide semiconductor film isexposed to plasma of a mixed gas of oxygen and hydrogen, hydrogen, arare gas, ammonia, and the like, oxygen vacancies are generated.Alternatively, when impurities are added to the oxide semiconductorfilm, oxygen vacancies can be formed while the impurities are added tothe oxide semiconductor film. The impurities can be added by an iondoping method, an ion implantation method, a plasma treatment method,and the like. In the plasma treatment method, plasma is generated in agas atmosphere containing the impurities to be added, and ions of theimpurities accelerated by plasma treatment are made to collide with theoxide semiconductor film, whereby oxygen vacancies can be formed in theoxide semiconductor film.

When an impurity, e.g., hydrogen is contained in the oxide semiconductorfilm in which oxygen vacancies are generated by addition of impurityelements, hydrogen enters an oxygen vacant site and forms a donor levelin the vicinity of the conduction band. As a result, the oxidesemiconductor film has increased conductivity to be a conductor. Anoxide semiconductor film that has become a conductor can be referred toas an oxide conductor film. That is, it can be said that thesemiconductor layer 140 is formed of an oxide semiconductor and theconductive layer 400 is formed of an oxide conductor film. It can alsobe said that the conductive layer 400 is formed of an oxidesemiconductor film having high conductivity or a metal oxide film havinghigh conductivity.

Note that the insulating layer 180 preferably contains hydrogen. Sincethe conductive layer 400 is in contact with the insulating layer 180,hydrogen contained in the insulating layer 180 can be diffused into theoxide semiconductor film formed at the same time as the semiconductorlayer 140. As a result, impurities can be added to the oxidesemiconductor film formed at the same time as the semiconductor layer140.

Furthermore, the insulating layer 170 is preferably formed using anoxide insulating film containing more oxygen than that in thestoichiometric composition, and the insulating layer 180 is preferablyformed using an insulating film containing hydrogen. When oxygencontained in the insulating layer 170 is transferred to thesemiconductor layer 140 of the transistor 50, the amount of oxygenvacancies in the semiconductor layer 140 can be reduced and a change inthe electrical characteristics of the transistor 50 can be reduced. Inaddition, hydrogen contained in the insulating layer 180 is transferredto the conductive layer 400 to increase the conductivity of theconductive layer 400.

In the above manner, the conductive layer 400 can be formed at the sametime as the semiconductor layer 140, and conductivity is given to theconductive layer 400 after the formation. Such a structure results in areduction in manufacturing costs.

Oxide semiconductor films generally have a visible light transmittingproperty because of their large energy gap. In contrast, an oxideconductor film is an oxide semiconductor film having a donor level inthe vicinity of the conduction band. Thus, the influence of lightabsorption due to the donor level is small, so that an oxide conductorfilm has a visible light transmitting property comparable to that of anoxide semiconductor film.

<<Conductive Layer 190>>

The conductive layer 190 is formed using a conductive film thattransmits visible light. For example, a material including one of indium(In), zinc (Zn), and tin (Sn) can be used for the conductive film thattransmits visible light. Typical examples of the conductive film thattransmits visible light include conductive oxides such as indium tinoxide, indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, indium zinc oxide, andindium tin oxide containing silicon oxide.

From the above, the conductive layer 190 and the conductive layer 400have light-transmitting properties; as a result, the capacitor 61 canhave a light-transmitting property as a whole.

<<Conductive Layer 380>>

The conductive layer 380 is formed using a conductive film thattransmits visible light. For example, a material including one of indium(In), zinc (Zn), and tin (Sn) can be used for the conductive film thattransmits visible light. Typical examples of the conductive film thattransmits visible light include conductive oxides such as indium tinoxide, indium oxide containing tungsten oxide, indium zinc oxidecontaining tungsten oxide, indium oxide containing titanium oxide,indium tin oxide containing titanium oxide, indium zinc oxide, andindium tin oxide containing silicon oxide.

<<Liquid Crystal Element 80>>

The liquid crystal element 80 can be driven in a fringe field switching(FFS) mode, for example. The alignment of liquid crystal moleculesincluded in the liquid crystal layer 390 can be controlled by anelectric field from the conductive layer 190; thus, the liquid crystallayer 390 functions as the liquid crystal element 80.

Although not illustrated in FIGS. 8A and 8B, an alignment film may beprovided on a side of the conductive layer 190 in contact with theliquid crystal layer 390 and on a side of the conductive layer 380 incontact with the liquid crystal layer 390.

Furthermore, the liquid crystal layer 390 is provided between theconductive layers 190 and 380, and the alignment of liquid crystalmolecules can be controlled by an electric field generated therebetween.Examples of a driving method of the display device including a liquidcrystal element include a TN mode, an STN mode, a VA mode, an axiallysymmetric aligned micro-cell (ASM) mode, an optically compensatedbirefringence (OCB) mode, a ferroelectric liquid crystal (FLC) mode, anantiferroelectric liquid crystal (AFLC) mode, an MVA mode, a patternedvertical alignment (PVA) mode, an in plane switching (IPS) mode, and atransverse bend alignment (TBA) mode. Other examples of the drivingmethod of the display device include an electrically controlledbirefringence (ECB) mode, a polymer dispersed liquid crystal (PDLC)mode, a polymer network liquid crystal (PNLC) mode, and a guest-hostmode. Note that one embodiment of the present invention is not limitedto the above, and various liquid crystal elements and driving methodscan be employed.

The liquid crystal element 80 may be formed using a liquid crystalcomposition including a liquid crystal exhibiting a nematic phase and achiral material. In that case, a cholesteric phase or a blue phase isexhibited. The liquid crystal exhibiting a blue phase has a shortresponse time of 1 msec or less. Since the liquid crystal exhibiting ablue phase is optically isotropic, alignment treatment is not necessaryand viewing angle dependence is small.

<<Light-Blocking Layer 18>>

A light-blocking material can be used for the light-blocking layer 18. Aresin in which a pigment is dispersed, a resin containing a dye, or aninorganic film such as a black chromium film can be used for thelight-blocking layer 18. Carbon black, an inorganic oxide, a compositeoxide containing a solid solution of a plurality of inorganic oxides, orthe like can be used for the light-blocking layer 18.

<<Coloring Layer 360>>

A coloring layer 360 transmits light in a specific wavelength range. Forexample, a color filter that transmits light in a specific wavelengthrange, such as red, green, blue, or yellow light, can be used. Eachcoloring layer is formed in a desired position with any of variousmaterials by a printing method, an inkjet method, an etching methodusing a photolithography method, or the like. In a white pixel, a resinsuch as a transparent resin or a white resin may overlap with thelight-emitting element.

<<Spacer 240>>

An insulating material can be used for a spacer 240. For example, aninorganic material, an organic material, or a stacked-layer material ofan inorganic material and an organic material can be used. Specifically,a film containing silicon oxide, silicon nitride, or the like, acrylic,polyimide, a photosensitive resin, or the like can be used.

<<Adhesive Layer 370>>

An inorganic material, an organic material, a composite material of aninorganic material and an organic material, or the like can be used forthe adhesive layer 370.

For example, an organic material such as a light curable adhesive, areactive curable adhesive, a thermosetting adhesive, and/or an anaerobicadhesive can be used for the adhesive layer 370. Note that each of theadhesives can be used alone or in combination.

The light curable adhesive refers to, for example, an adhesive that iscured by ultraviolet rays, an electron beam, visible light, infraredlight, or the like.

Specifically, an adhesive containing an epoxy resin, an acrylic resin, asilicone resin, a phenol resin, a polyimide resin, an imide resin, apolyvinyl chloride (PVC) resin, a polyvinyl butyral (PVB) resin, anethylene vinyl acetate (EVA) resin, silica, or the like can be used forthe adhesive layer 370.

The material is cured rapidly particularly when a light curable adhesiveis used, leading to shortening of the process time. In addition,influence of the film formation step can be inhibited because curingstarts with light irradiation. In addition, involuntary curing of theadhesive due to environment can be prevented because curing starts withlight irradiation. Furthermore, curing can be performed at lowtemperatures to facilitate the control of process environment. From theabove reasons, the use of a light curable adhesive shortens the processtime and reduces processing costs.

<<Insulating Layer 330>>

The insulating layer 330 has a function of making a flat surface. Aninorganic material or an organic material can be used for the insulatinglayer 330. For example, an oxide insulating film of silicon oxide,silicon oxynitride, aluminum oxide, aluminum oxynitride, gallium oxide,gallium oxynitride, yttrium oxide, yttrium oxynitride, hafnium oxide,hafnium oxynitride, or the like; a nitride insulating film of siliconnitride, aluminum nitride, or the like; or a heat-resistant organicmaterial such as a polyimide resin, an acrylic resin, a polyimide amideresin, a benzocyclobutene resin, a polyamide resin, or an epoxy resincan be used.

<<FPC 42>>

The FPC 42 is electrically connected to the conductive layer 160 throughan anisotropic conductive film 510. The conductive layer 160 can beformed in a step of forming electrode layers of the transistor 50 andthe like. An image signal and the like can be supplied from the FPC 42to the driver circuit including the transistor 50, the capacitor 61, andthe like.

>>Another Structure of Edge Shape of Substrate of Display Device<<

In addition, FIG. 9 shows a cross-sectional view of another structure ofthe display device in FIGS. 8A and 8B. The edge of the substrate has nounevenness as illustrated in FIG. 1C, and a protective film can bedeposited by an ALD method.

<<Other Structures of Protective Film 23 Formed in Display Device 10>>

When a protective film is formed in the display device 10, theprotective film can be formed on the surface and the side surfaceselectively. FIG. 10, FIG. 11, and FIG. 12 show cross-sectional views ofthe display device.

In FIG. 10 and FIG. 11, as illustrated in FIG. 2A, a structure where aprotective film is not formed outside the substrates 100 and 300 byusing masking can be employed. For example, in FIG. 10, the formation ofthe protective film on a rear surface of the substrate 100 and a topsurface side of the substrate 100 in the vicinity of the FPC 42 can beinhibited. In FIG. 11, the formation of the protective film on bothsurface sides of a rear surface of the substrate 100 and a top surfaceof the substrate 300 can be inhibited. In these cases, the protectivefilm may be deposited around the edge portions of the substrates 100 and300 as in a region 13. Alternatively, as illustrated in FIG. 12, theregion 14 where a protective film is not formed on the rear surface sideof the substrate 100 can be provided by the method shown in FIGS. 4A to4D.

<<Combination of Display Device and Touch Sensor>>

The display device is combined with a touch sensor, whereby a touchpanel can be formed. FIG. 13, FIG. 14, and FIG. 15 are each across-sectional view of a touch panel. Electrodes (wirings) for thetouch sensor can be formed using a conductive layer 410, a conductivelayer 430, an insulating layer 420, and an insulating layer 440.Alternatively, for the wiring for the touch sensor, the conductivelayers 190 and 380 used in the display panel can be used, and a touchsensor can be formed by combining the conductive layers 190 and 380. Theelectrode for the touch sensor may be formed on the side of thesubstrate 300 viewed by a viewer (the surface side) or may be formedinside (on the display element side).

<<Structure Example of Sensor Electrode and the Like>>

More specific structure examples of an input device 90, which functionsas a touch sensor, are described below with reference to drawings.

FIG. 16A is a schematic top view of the input device 90. The inputdevice 90 includes a plurality of electrodes 931, a plurality ofelectrodes 932, a plurality of wirings 941, and a plurality of wirings942 over a substrate 930. The substrate 930 is provided with an FPC 950which is electrically connected to each of the plurality of wirings 941and the plurality of wirings 942. FIG. 16A illustrates an example inwhich the FPC 950 is provided with an IC 951.

FIG. 16B shows an enlarged view of a region surrounded by a dasheddotted line in FIG. 16A. The electrodes 931 are each in the form of aseries of rhombic electrode patterns aligned in a lateral direction ofthis figure. The rhombic electrode patterns aligned in a line areelectrically connected to each other. The electrodes 932 are also eachin the form of a series of rhombic electrode patterns aligned in alongitudinal direction of this figure and the rhombic electrode patternsaligned in a line are electrically connected. Part of the electrode 931and part of the electrode 932 overlap and intersect with each other. Atthis intersection portion, an insulator is sandwiched in order to avoidan electrical short-circuit between the electrode 931 and the electrode932.

As shown in FIG. 16C, the electrodes 932 may form a plurality ofisland-shape rhombic electrodes 933 and bridge electrodes 934. Theelectrodes 933 are aligned in a longitudinal direction of this figure,and two adjacent electrodes 933 are electrically connected to each otherby the bridge electrode 934. Such a structure makes it possible that theelectrodes 933 and the electrodes 931 can be formed at the same time byprocessing the same conductive film. This can prevent variations in thethickness of these films, and can prevent the resistance value and thelight transmittance of each electrode from varying from place to place.Note that although the electrodes 932 include the bridge electrodes 934here, the electrodes 931 may have such a structure.

As shown in FIG. 16D, a design in which rhombic electrode patterns ofthe electrodes 931 and 932 shown in FIG. 16B are hollowed out and onlyedge portions are left may be used. At that time, when the electrodes931 and the electrodes 932 are too small in width for the users to view,the electrodes 931 and the electrodes 932 can be formed using alight-blocking material such as a metal or an alloy, as described later.In addition, either the electrodes 931 or the electrodes 932 shown inFIG. 16D may include the above bridge electrodes 934.

One of the electrodes 931 is electrically connected to one of thewirings 941. One of the electrodes 932 is electrically connected to oneof the wirings 942. Here, one of the electrodes 931 and 932 correspondsto the row wiring, and the other corresponds to the column wiring.

As examples, enlarged schematic views of part of the electrodes 931 orthe electrodes 932 are shown in FIGS. 17A to 17D. The electrodes canhave various shapes.

FIGS. 18A to 18C illustrate examples of the case where electrodes 936and electrodes 937, which have a top surface shape of thin lines, areused instead of the electrodes 931 and the electrodes 932. FIG. 18Ashows an example in which linear electrodes 936 and 937 are arranged soas to form a lattice shape. In FIGS. 18B and 18C, the electrodes 936 and937 having a zigzag shape are arranged.

FIGS. 19A to 19C show enlarged views of a region surrounded by a dasheddotted line in FIG. 18B, and FIGS. 19D to 19F show enlarged views of aregion surrounded by a dashed dotted line in FIG. 18C. In thesedrawings, the electrodes 936, the electrodes 937, and intersectionportions 938 at which the electrodes 936 and the electrodes 937intersect are illustrated. The straight-line portions of the electrodes936 and the electrodes 937 shown in FIGS. 19A and 19D may have aserpentine shape that meanders with angled corners as shown in FIGS. 19Band 19E or may have a serpentine shape that continuously meanders asshown in FIGS. 19C and 19F.

<<Structure Example of In-Cell Touch Panel>>

A structure example of a touch panel incorporating the touch sensor intoa display portion including a plurality of pixels will be describedbelow. Here, an example where a liquid crystal element is used as adisplay element provided in the pixel is shown.

FIG. 20A is an equivalent circuit diagram of part of a pixel circuitprovided in the display portion of the touch panel exemplified in thisstructure example.

Each pixel includes at least a transistor 3503 and a liquid crystalelement 3504. In addition, a gate of the transistor 3503 is electricallyconnected to a wiring 3501 and one of a source and a drain of thetransistor 3503 is electrically connected to a wiring 3502.

The pixel circuit includes a plurality of wirings extending in the Xdirection (e.g., a wiring 3510_1 and a wiring 3510_2) and a plurality ofwirings extending in the Y direction (e.g., a wiring 3511). They areprovided to intersect with each other, and capacitance is formedtherebetween.

Among the pixels provided in the pixel circuit, electrodes of the liquidcrystal elements of some pixels adjacent to each other are electricallyconnected to each other to form one block. The block is classified intotwo types: an island-shaped block (e.g., a block 3515_1 or a block3515_2) and a linear block (e.g., a block 3516) extending in the Ydirection. Note that only part of the pixel circuit is illustrated inFIGS. 20A and 20B, and actually, these two kinds of blocks arerepeatedly arranged in the X direction and the Y direction.

The wiring 3510_1 (or the wiring 3510_2) extending in the X direction iselectrically connected to the island-shaped block 3515_1 (or the block3515_2). Although not illustrated, the wiring 3510_1 extending in the Xdirection is electrically connected to a plurality of island-shapedblocks 3515_1 which are provided discontinuously along the X directionwith the linear blocks therebetween. Furthermore, the wiring 3511extending in the Y direction is electrically connected to the linearblock 3516.

FIG. 20B is an equivalent circuit diagram illustrating the connectionbetween a plurality of wirings 3510 extending in the X direction and theplurality of wirings 3511 extending in the Y direction. Input voltage ora common potential can be input to each of the wirings 3510 extending inthe X direction. Furthermore, a ground potential can be input to each ofthe wirings 3511 extending in the Y direction, or each of the wirings3511 can be electrically connected to a detection circuit.

Operation of the above-described touch panel will be described belowwith reference to FIGS. 21A and 21B.

Here, one frame period is divided into a writing period and a sensingperiod. The writing period is a period in which image data is written toa pixel, and the wirings 3510 (also referred to as gate lines) aresequentially selected. On the other hand, the sensing period is a periodin which sensing is performed by a touch sensor, and the wirings 3510extending in the X direction are sequentially selected and input voltageis input.

FIG. 21A is an equivalent circuit diagram in the writing period. In thewiring period, a common potential is input to both the wiring 3510extending in the X direction and the wiring 3511 extending in the Ydirection.

FIG. 21B is an equivalent circuit diagram at some point in time in thesensing period. In the sensing period, each of the wirings 3511extending in the Y direction is electrically connected to the detectioncircuit. Input voltage is input to the wirings 3510 extending in the Xdirection which are selected, and a common potential is input to thewirings 3510 extending in the X direction which are not selected.

Note that the driving method described here can be applied to not onlyan in-cell touch panel but also the above-described touch panels, andcan be used in combination with the method described in the drivingmethod example.

It is preferable that a period in which an image is written and a periodin which sensing is performed by a touch sensor be separately providedas described above. Thus, a decrease in sensitivity of the touch sensorcaused by noise generated when data is written to a pixel can besuppressed.

<<Conductive Layer 410, 430>>

The conductive layer 410 is formed using a metal element selected fromaluminum, chromium, copper, tantalum, titanium, molybdenum, nickel,iron, cobalt, and tungsten; an alloy containing any of these metalelements as a component; an alloy containing any of these metal elementsin combination; or the like. Further, one or more metal elementsselected from manganese and zirconium may be used. The conductive layer410 may have a single-layer structure or a layered structure of two ormore layers. For example, any of the following can be used: asingle-layer structure of an aluminum film containing silicon; asingle-layer structure of a copper film containing manganese; atwo-layer structure in which a titanium film is stacked over an aluminumfilm; a two-layer structure in which a titanium film is stacked over atitanium nitride film; a two-layer structure in which a tungsten film isstacked over a titanium nitride film; a two-layer structure in which atungsten film is stacked over a tantalum nitride film or a tungstennitride film; a two-layer structure in which a copper film is stackedover a copper film containing manganese; a three-layer structure inwhich a titanium film, an aluminum film, and a titanium film are stackedin this order; a three-layer structure in which a copper film containingmanganese, a copper film, and a copper film containing manganese arestacked in this order; and the like. Alternatively, an alloy film or anitride film which contains aluminum and one or more elements selectedfrom titanium, tantalum, tungsten, molybdenum, chromium, neodymium, andscandium may be used. Alternatively, as a material of the conductivefilms such as the conductive layer 410, that is, wirings and electrodesforming the touch panel, a transparent conductive film containing indiumoxide, tin oxide, zinc oxide, or the like (e.g., ITO) can be given.Moreover, for example, a low-resistance material is preferably used asthe material of the wiring and the electrode in the touch panel. Forexample, silver, copper, aluminum, a carbon nanotube, graphene, or ametal halide (such as a silver halide) may be used. Alternatively, ametal nanowire including a plurality of conductors with an extremelysmall width (e.g., a diameter of several nanometers) may be used.Further alternatively, a net-like metal mesh with a conductor may beused. Examples of such materials include an Ag nanowire, a Cu nanowire,an Al nanowire, an Ag mesh, a Cu mesh, and an Al mesh. For example, inthe case of using an Ag nanowire for the wiring and the electrode in thetouch panel, a visible light transmittance of 89% or more and a sheetresistance of 40 Ω/sq. or more and 100 Ω/sq. or less can be achieved. Ametal nanowire, a metal mesh, a carbon nanotube, graphene, and the like,which are examples of a material that can be used for theabove-described wiring and electrode in the touch panel, have a highvisible light transmittance; therefore, they may be used for anelectrode of a display element (e.g., a pixel electrode or a commonelectrode). The conductive layer 430 can be formed using a film similarto that used to form the conductive layer 410.

<<Insulating Layer 420 and Insulating Layer 440>>

An inorganic material or an organic material can be used for theinsulating layer 420. For example, an oxide insulating film of siliconoxide, silicon oxynitride, aluminum oxide, aluminum oxynitride, galliumoxide, gallium oxynitride, yttrium oxide, yttrium oxynitride, hafniumoxide, hafnium oxynitride, or the like; a nitride insulating film ofsilicon nitride, aluminum nitride, or the like; or a heat-resistantorganic material such as a polyimide resin, an acrylic resin, apolyimide amide resin, a benzocyclobutene resin, a polyamide resin, oran epoxy resin can be used. The insulating layer 440 can be formed usinga film similar to that used for the insulating layer 420.

<<Organic EL Panel>>

Furthermore, the display device 10 where a light-emitting element 70 isused as a display element can be fabricated.

FIG. 22, FIG. 23, and FIG. 24 are each a cross-sectional view of adisplay device using a light-emitting element. A portion that is alsoincluded in a liquid crystal panel, such as a transistor, can be formedin a manner similar to that of the liquid crystal panel.

<<Light-Emitting Element 70>>

As the light-emitting element 70, a self-luminous element can be used,and an element whose luminance is controlled by current or voltage isincluded in the category of the light-emitting element. For example, alight-emitting diode (LED), an organic EL element, an inorganic ELelement, or the like can be used. For example, an organic element whichincludes a lower electrode, an upper electrode, and a layer (alsoreferred to as an EL layer 250) containing a light-emitting organiccompound between the lower electrode and the upper electrode can be usedas the light-emitting element 70.

The light-emitting element may be a top emission, bottom emission, ordual emission light-emitting element. A conductive film that transmitsvisible light is used as the electrode through which light is extracted.A conductive film that reflects visible light is preferably used as theelectrode through which light is not extracted.

When a voltage higher than the threshold voltage of the light-emittingelement is applied between a lower electrode including a conductivelayer 220 and an upper electrode including a conductive layer 260, holesare injected to the EL layer 250 from the anode side and electrons areinjected to the EL layer 250 from the cathode side. The injectedelectrons and holes are recombined in the EL layer 250 and alight-emitting substance contained in the EL layer 250 emits light.

The EL layer 250 includes at least a light-emitting layer. In additionto the light-emitting layer, the EL layer 250 may further include one ormore layers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with a high electron- andhole-transport property), and the like.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer 250, and an inorganic compound may be used. Each of thelayers included in the EL layer 250 can be formed by any of thefollowing methods: an evaporation method (including a vacuum evaporationmethod), a transfer method, a printing method, an inkjet method, acoating method, and the like.

The light-emitting element may contain two or more kinds oflight-emitting substances. Thus, for example, a light-emitting elementthat emits white light can be achieved. For example, light-emittingsubstances are selected so that two or more light-emitting substancesemit complementary colors to obtain white light emission. Alight-emitting substance that emits red (R) light, green (G) light, blue(B) light, yellow (Y) light, or orange (O) light or a light-emittingsubstance that emits light containing spectral components of two or moreof R light, G light, and B light can be used, for example Alight-emitting substance that emits blue light and a light-emittingsubstance that emits yellow light may be used, for example. At thistime, the emission spectrum of the light-emitting substance that emitsyellow light preferably contains spectral components of G light and Rlight. The emission spectrum of the light-emitting element 70 preferablyhas two or more peaks in the wavelength range in a visible region (e.g.,greater than or equal to 350 nm and less than or equal to 750 nm orgreater than or equal to 400 nm and less than or equal to 800 nm).

The EL layer 250 may include a plurality of light-emitting layers. Inthe EL layer 250, the plurality of light-emitting layers may be stackedin contact with one another or may be stacked with a separation layerprovided therebetween. The separation layer may be provided between afluorescent layer and a phosphorescent layer, for example.

The separation layer can be provided, for example, to prevent energytransfer by the Dexter mechanism (particularly triplet energy transfer)from a phosphorescent material or the like in an excited state which isgenerated in the phosphorescent layer to a fluorescent material or thelike in the fluorescent layer. The thickness of the separation layer maybe several nanometers. Specifically, the thickness of the separationlayer may be greater than or equal to 0.1 nm and less than or equal to20 nm, greater than or equal to 1 nm and less than or equal to 10 nm, orgreater than or equal to 1 nm and less than or equal to 5 nm. Theseparation layer contains a single material (preferably, a bipolarsubstance) or a plurality of materials (preferably, a hole-transportmaterial and an electron-transport material).

The separation layer may be formed using a material contained in alight-emitting layer in contact with the separation layer. Thisfacilitates the manufacture of the light-emitting element and reducesthe drive voltage. For example, in the case where the phosphorescentlayer contains a host material, an assist material, and thephosphorescent material (a guest material), the separation layer maycontain the host material and the assist material. In other words, theseparation layer includes a region not containing the phosphorescentmaterial and the phosphorescent layer includes a region containing thephosphorescent material in the above structure. Accordingly, theseparation layer and the phosphorescent layer can be evaporatedseparately depending on whether a phosphorescent material is used ornot. With such a structure, the separation layer and the phosphorescentlayer can be formed in the same chamber. Thus, the manufacturing costcan be reduced.

<<Microcavity>>

The light-emitting element 70 in FIG. 22 is an example of alight-emitting element having a microcavity structure. For example, themicrocavity structure may be formed using the lower electrode and theupper electrode of the light-emitting element 70 so that light with aspecific wavelength can be extracted from the light-emitting elementefficiently.

Specifically, a reflective film which reflects visible light is used asthe lower electrode, and a semi-transmissive and semi-reflective filmwhich transmits part of visible light and reflects part of visible lightis used as the upper electrode. The upper electrode and the lowerelectrode are arranged so that light with a specific wavelength can beextracted efficiently.

The lower electrode functions as, for example, a lower electrode or ananode of the light-emitting element. The lower electrode has a functionof adjusting the optical path length so that desired light emitted fromlight-emitting layers resonates and its wavelength can be amplified. Alayer 230 that adjusts the optical path length is not necessarilyprovided in the lower electrode. At least one layer included in thelight-emitting element can be used to adjust the optical path length.The layer 230 that adjusts the optical path length can be formed using,for example, indium oxide, indium tin oxide (ITO), indium zinc oxide,zinc oxide (ZnO), or zinc oxide to which gallium is added.

In the case of using the microcavity structure, a semi-transmissive andsemi-reflective electrode can be used as the upper electrode of thelight-emitting element. The semi-transmissive semi-reflective electrodeis formed using a reflective conductive material and alight-transmitting conductive material. As the conductive materials, aconductive material having a visible light reflectivity of higher thanor equal to 20% and lower than or equal to 80%, preferably higher thanor equal to 40% and lower than or equal to 70%, and a resistivity oflower than or equal to 1×10⁻² Ω·cm can be used. The semi-transmissivesemi-reflective electrode can be formed using one or more kinds ofconductive metals, conductive alloys, conductive compounds, and thelike. In particular, a material with a small work function (3.8 eV orless) is preferable. For example, aluminum, silver, an element belongingto Group 1 or 2 of the periodic table (e.g., an alkali metal such aslithium or cesium, an alkaline earth metal such as calcium or strontium,or magnesium), an alloy containing any of these elements (e.g., Ag—Mg orAl—Li), a rare earth metal such as europium or ytterbium, and an alloycontaining any of these rare earth metals.

The electrodes can each be formed by an evaporation method or asputtering method. Alternatively, a discharging method such as anink-jet method, a printing method such as a screen printing method, or aplating method may be used.

Note that an organic EL can employ a structure other than a microcavitystructure. For example, a separate coloring method by which differentcolors are emitted from light-emitting elements, or a white EL method inwhich a material emitting white light is used can be employed.

<<Conductive Layer 200>>

The conductive layer 200 is formed using a metal element selected fromaluminum, chromium, copper, tantalum, titanium, molybdenum, nickel,iron, cobalt, and tungsten; an alloy containing any of these metalelements as a component; an alloy containing any of these metal elementsin combination; or the like. Further, one or more metal elementsselected from manganese and zirconium may be used. The conductive layer200 may have a single-layer structure or a layered structure of two ormore layers. For example, any of the following can be used: asingle-layer structure of an aluminum film containing silicon; asingle-layer structure of a copper film containing manganese; atwo-layer structure in which a titanium film is stacked over an aluminumfilm; a two-layer structure in which a titanium film is stacked over atitanium nitride film; a two-layer structure in which a tungsten film isstacked over a titanium nitride film; a two-layer structure in which atungsten film is stacked over a tantalum nitride film or a tungstennitride film; a two-layer structure in which a copper film is stackedover a copper film containing manganese; a three-layer structure inwhich a titanium film, an aluminum film, and a titanium film are stackedin this order; a three-layer structure in which a copper film containingmanganese, a copper film, and a copper film containing manganese arestacked in this order; and the like. Alternatively, an alloy film or anitride film which contains aluminum and one or more elements selectedfrom titanium, tantalum, tungsten, molybdenum, chromium, neodymium, andscandium may be used.

<<Conductive Layer 220>>

For the conductive layer 220 that reflects visible light, for example, ametal material such as aluminum, gold, platinum, silver, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or analloy containing any of these metal materials can be used. Lanthanum,neodymium, germanium, or the like may be added to the metal material orthe alloy. Furthermore, an alloy containing aluminum (an aluminum alloy)such as an alloy of aluminum and titanium, an alloy of aluminum andnickel, an alloy of aluminum and neodymium, or an alloy of aluminum,nickel, and lanthanum (Al—Ni—La), or an alloy containing silver such asan alloy of silver and copper, an alloy of silver, palladium, and copper(Ag—Pd—Cu, also referred to as APC), or an alloy of silver and magnesiumcan be used for the conductive film. An alloy of silver and copper ispreferable because of its high heat resistance. A metal film or a metaloxide film is stacked on an aluminum alloy film, whereby oxidation ofthe aluminum alloy film can be suppressed. Examples of a material forthe metal film or the metal oxide film are titanium and titanium oxide.Alternatively, the conductive film having a property of property oftransmitting visible light and a film containing any of the above metalmaterials may be stacked. For example, a stacked film of silver and ITOor a stacked film of an alloy of silver and magnesium and ITO can beused.

<<Conductive Layer 260>>

The conductive layer 260 that transmits visible light can be formedusing, for example, indium oxide, indium tin oxide (ITO), indium zincoxide, zinc oxide (ZnO), or zinc oxide to which gallium is added.Alternatively, a film of a metal material such as gold, silver,platinum, magnesium, nickel, tungsten, chromium, molybdenum, iron,cobalt, copper, palladium, or titanium; an alloy containing any of thesemetal materials; or a nitride of any of these metal materials (e.g.,titanium nitride) can be formed thin so as to have a light-transmittingproperty. A stack of any of the above materials can be used as theconductive layer. For example, a stacked film of ITO and an alloy ofsilver and magnesium is preferably used, in which case conductivity canbe increased. Further alternatively, graphene or the like may be used.

<<Organic EL Panel Using Separate Coloring Method>>

An organic EL element can be formed using a separate coloring method asillustrated in FIG. 23. FIG. 23 is different from FIG. 22 in that aseparate coloring method is used for the EL layer 250 over theconductive layer 220.

<<Flexible Display Device>>

The display device may be formed over a flexible substrate 101 or aflexible substrate 301 as illustrated in FIG. 24. The flexible substrateand the display device can be bonded to each other with the adhesivelayer 370. In this manner, a flexible touch panel that can be folded ora touch panel having a curved surface can be fabricated. Moreover, thethickness of the substrate can be small, leading to a reduction inweight of the touch panel.

<<Manufacturing Method Example of Flexible Display Device>>

Here, a method for manufacturing a flexible display device will bedescribed.

For convenience, a structure including a pixel and a circuit, astructure including an optical member such as a color filter, or astructure including a touch sensor is referred to as an element layer.An element layer includes a display element, for example, and mayinclude a wiring electrically connected to the display element or anelement such as a transistor used in a pixel or a circuit in addition tothe display element.

Here, a support body (e.g., the substrate 101 or the substrate 301) withan insulating surface where an element layer is formed is referred to asa base material.

As a method for forming an element layer over a flexible base materialprovided with an insulating surface, there are a method in which anelement layer is formed directly over the base material, and a method inwhich an element layer is formed over a supporting base material that isdifferent from the base material and has stiffness and then the elementlayer is separated from the supporting base material and transferred tothe base material.

In the case where a material of the base material can withstand heatingtemperature in a process for forming the element layer, it is preferablethat the element layer be formed directly over the base material, inwhich case a manufacturing process can be simplified. At this time, theelement layer is preferably formed in a state where the base material isfixed to the supporting base material, in which case transfer thereof inan apparatus and between apparatuses can be easy.

In the case of employing the method in which the element layer is formedover the supporting base material and then transferred to the basematerial, first, a separation layer and an insulating layer are stackedover the supporting base material, and then the element layer is formedover the insulating layer. Next, the element layer is separated from thesupporting base material and then transferred to the base material. Atthis time, a material is selected that would causes separation at aninterface between the supporting base material and the separation layer,at an interface between the separation layer and the insulating layer,or in the separation layer.

For example, it is preferable that a stacked layer of a layer includinga high-melting-point metal material, such as tungsten, and a layerincluding an oxide of the metal material be used as the separationlayer, and a stacked layer of a plurality of layers, such as a siliconnitride layer and a silicon oxynitride layer be used over the separationlayer. The use of the high-melting-point metal material is preferablebecause the degree of freedom of the process for forming the elementlayer can be increased.

The separation may be performed by application of mechanical power, byetching of the separation layer, by dripping of a liquid into part ofthe separation interface to penetrate the entire separation interface,or the like. Alternatively, separation may be performed by heating theseparation interface by utilizing a difference in thermal expansioncoefficient.

The separation layer is unnecessary in the case where separation canoccur at an interface between the supporting base material and theinsulating layer. For example, glass is used as the supporting basematerial and an organic resin such as polyimide is used as theinsulating layer, a separation trigger is formed by locally heating partof the organic resin by laser light or the like, and separation isperformed at an interface between the glass and the insulating layer.Alternatively, a metal layer may be provided between the supporting basematerial and the insulating layer formed of an organic resin, andseparation may be performed at the interface between the metal layer andthe insulating layer by heating the metal layer by feeding a current tothe metal layer. In that case, the insulating layer formed of an organicresin can be used as a base material.

Examples of such a base material having flexibility include polyesterresins such as polyethylene terephthalate (PET) and polyethylenenaphthalate (PEN), a polyacrylonitrile resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin, a cycloolefin resin, apolystyrene resin, a polyamide imide resin, and a polyvinyl chlorideresin. In particular, it is preferable to use a material with a lowthermal expansion coefficient, and for example, a polyamide imide resin,a polyimide resin, PET, or the like with a thermal expansion coefficientlower than or equal to 30×10⁻⁶/K can be suitably used. A substrate inwhich a fibrous body is impregnated with a resin (also referred to asprepreg) or a substrate whose thermal expansion coefficient is reducedby mixing an inorganic filler with an organic resin can also be used.

In the case where a fibrous body is included in the above material, ahigh-strength fiber of an organic compound or an inorganic compound isused as the fibrous body. The high-strength fiber is specifically afiber with a high tensile elastic modulus or a fiber with a high Young'smodulus. Typical examples thereof include a polyvinyl alcohol basedfiber, a polyester based fiber, a polyamide based fiber, a polyethylenebased fiber, an aramid based fiber, a polyparaphenylene benzobisoxazolefiber, a glass fiber, and a carbon fiber. As the glass fiber, glassfiber using E glass, S glass, D glass, Q glass, or the like can be used.These fibers may be used in a state of a woven fabric or a nonwovenfabric, and a structure body in which this fibrous body is impregnatedwith a resin and the resin is cured may be used as the flexiblesubstrate. The structure body including the fibrous body and the resinis preferably used as the flexible substrate, in which case thereliability against bending or breaking due to local pressure can beincreased.

Alternatively, glass, metal, or the like that is thin enough to haveflexibility can be used as the base material. Alternatively, a compositematerial where glass and a resin material are attached to each other maybe used.

In the structure shown in FIG. 24, for example, a first separation layerand an insulating layer 112 are formed in this order over a firstsupporting base material, and then components in a layer over the firstseparation layer and the insulating layer 112 are formed. Separately, asecond separation layer and an insulating layer 312 are formed in thisorder over a second supporting base material, and then upper componentsare formed. Next, the first supporting base material is bonded to thesecond supporting base material with the adhesive layer 370. After that,separation at an interface between the second separation layer and theinsulating layer 312 is conducted so that the second supporting basematerial and the second separation layer are removed, and then thesubstrate 301 is bonded to the insulating layer 312 using an adhesivelayer 372. Furthermore, separation at an interface between the firstseparation layer and the insulating layer 112 is conducted so that thefirst supporting base material and the first separation layer areremoved, and then the substrate 101 is bonded to the insulating layer112 using an adhesive layer 371. Note that either side may be subjectedto separation and attachment first.

The above is the description of a manufacturing method of a flexibledisplay device.

<<Positional Relationship Between Transistor and Wirings of TouchSensor>>

FIG. 25 is a top view illustrating the positional relationship betweenthe pixel, a transistor, and wirings of the touch sensor. The conductivelayer 410, which is an electrode for the touch sensor, can be providedso as to overlap with a source line 91 or a gate line 92, or can beprovided not to overlap with and parallel to the source line 91 or thegate line 92, for example. The conductive layer 410, which is a wiringof the touch sensor, may overlap with a transistor 50 and a capacitor 61unlike in the example. Although the conductive layer 410 is provided notto overlap with the pixel 24, the conductive layer 410 can be providedto overlap with the pixel 24. The conductive layers 430 and 380 whichcan function as an electrode of the touch sensor can be arranged in asimilar manner.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 5

Described in this embodiment is a modification example of the structureof the transistor described in Embodiment 4.

<<Stacked Oxide Semiconductor>>

Note that in the semiconductor layer 140, a plurality of oxidesemiconductor films that differ in the atomic ratio of metal elementsmay be stacked. For example, as in a transistor 51 in FIG. 26A, an oxidesemiconductor layer 141 and an oxide semiconductor layer 142 may bestacked in this order over the insulating layer 130. Alternatively, asillustrated in FIG. 26B, the oxide semiconductor layer 142, the oxidesemiconductor layer 141, and an oxide semiconductor layer 143 may bestacked in this order over the insulating layer 130. The oxidesemiconductor layers 142 and 143 differ from the oxide semiconductorlayer 141 in the atomic ratio of metal elements.

<<Channel-Protective Transistor and Top-Gate Transistor>>

The transistor 50 and the like illustrated in FIG. 8B are, but are notlimited to, bottom-gate transistors. FIG. 27A illustrates a transistor53 and FIG. 27B illustrates a transistor 54 as modification examples ofthe transistor 50. Although the transistor 50 illustrated in FIG. 8B isa channel-etched transistor, it may be the channel-protective transistor53 including an insulating layer 165 as illustrated in thecross-sectional view of FIG. 27A or may be the top-gate transistor 54 asillustrated in the cross-sectional view of FIG. 27B.

<<Dual-Gate Transistor>>

A transistor 55, which is a modification example of the transistor 50,will be described with reference to FIGS. 28A to 28C. The transistorillustrated in FIGS. 28A to 28C has a dual-gate structure.

FIGS. 28A to 28C are a top view and cross-sectional views of thetransistor 55. FIG. 28A is a top view of the transistor 55, FIG. 28B isa cross-sectional view taken along dashed-dotted line A-A′ in FIG. 28A,and FIG. 28C is a cross-sectional view taken along dashed-dotted lineB-B′ in FIG. 28A. Note that in FIG. 28A, the substrate 100, theinsulating layer 110, the insulating layer 130, the insulating layer170, the insulating layer 180, and the like are not illustrated for thesake of clarity.

The transistor 55 illustrated in FIGS. 28A to 28C includes theconductive layer 120 functioning as a gate electrode over the insulatinglayer 110, the insulating layer 130 functioning as a gate insulatingfilm over the conductive layer 120, the semiconductor layer 140overlapping with the conductive layer 120 with the insulating layer 130provided therebetween, the conductive layers 150 and 160 in contact withthe semiconductor layer 140, the insulating layer 170 over thesemiconductor layer 140 and the conductive layers 150 and 160, theinsulating layer 180 over the insulating layer 170, and a conductivelayer 520 functioning as a back gate electrode over the insulating layer180. The conductive layer 120 is connected to the conductive layer 520in an opening 530 in the insulating layers 130, 170, and 180.

<<Conductive Layer 520>>

The conductive layer 520 is formed using a conductive film thattransmits visible light or a conductive film that reflects visiblelight. For example, a material including one of indium (In), zinc (Zn),and tin (Sn) can be used for the conductive film that transmits visiblelight. Typical examples of the conductive film that transmits visiblelight include conductive oxides such as indium tin oxide, indium oxidecontaining tungsten oxide, indium zinc oxide containing tungsten oxide,indium oxide containing titanium oxide, indium tin oxide containingtitanium oxide, indium zinc oxide, and indium tin oxide containingsilicon oxide. For the conductive film that reflects visible light, amaterial containing aluminum or silver can be used, for example.

Note that when a side surface of the semiconductor layer 140 faces theconductive layer 520 in the channel width direction as shown in FIG.28C, carriers flow not only at the interface between the insulatinglayer 170 and the semiconductor layer 140 and at the interface betweenthe insulating layer 130 and the semiconductor layer 140 but also in thesemiconductor layer 140. Therefore, the amount of transfer of carriersin the transistor 55 is increased. As a result, the on-state current andfield-effect mobility of the transistor 55 are increased. The electricfield of the conductive layer 520 affects the side surface or an endportion including the side surface and its vicinity of the semiconductorlayer 140; thus, generation of a parasitic channel at the side surfaceor the end portion of the semiconductor layer 140 can be suppressed.

By providing the transistor illustrated in FIGS. 28A to 28C in a pixelportion, signal delay in wirings can be reduced and display defects suchas display unevenness can be suppressed even though the number ofwirings is increased in a large-sized display device or ahigh-resolution display device.

Note that all of transistors 52 included in the peripheral circuit (gatedriver and the like) may have the same structure or may have two or morekinds of structures. All of a plurality of transistors 50 included inthe pixel portion may have the same structure, or may have two or morekinds of structures.

Although an example of using a transistor including an oxidesemiconductor is shown in this embodiment, one embodiment of the presentinvention is not limited to this example Depending on the case orcircumstances, a transistor including a semiconductor material that isnot an oxide semiconductor may be used in one embodiment of the presentinvention.

For example, a transistor in which a Group 14 element, a compoundsemiconductor, an oxide semiconductor, or the like is used for thesemiconductor layer 140 can be used. Specifically, a semiconductorcontaining silicon, a semiconductor containing gallium arsenide, anorganic semiconductor, or the like can be used.

For example, single crystal silicon, polysilicon, or amorphous siliconcan be used for the semiconductor layer of the transistor.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 6

In this embodiment, a structure example of the display panel of oneembodiment of the present invention will be described with reference toFIGS. 29A to 29C.

[Structure Example]

FIG. 29A is a top view of the display device of one embodiment of thepresent invention. FIG. 29B is a circuit diagram illustrating a pixelcircuit that can be used in the case where a liquid crystal element isused in a pixel in the display device of one embodiment of the presentinvention. FIG. 29C is a circuit diagram illustrating a pixel circuitthat can be used in the case where an organic EL element is used in apixel in the display device of one embodiment of the present invention.

The transistor in the pixel portion can be formed in accordance with theabove embodiments. The transistor can be easily formed as an n-channeltransistor, and thus part of a driver circuit that can be formed usingan n-channel transistor is formed over the same substrate as thetransistor of the pixel portion. With the use of any of the transistorsdescribed in the above embodiments for the pixel portion or the drivercircuit in this manner, a highly reliable display device can beprovided.

FIG. 29A illustrates an example of a top view of an active matrixdisplay device. A pixel portion 701, a scan line driver circuit 702, ascan line driver circuit 703, and a signal line driver circuit 704 areformed over a substrate 700 of the display device. In the pixel portion701, a plurality of signal lines extended from the signal line drivercircuit 704 are arranged and a plurality of scan lines extended from thescan line driver circuit 702 and the scan line driver circuit 703 arearranged. Note that pixels which include display elements are providedin a matrix in respective regions where the scan lines and the signallines intersect with each other. The substrate 700 of the display deviceis connected to a timing control circuit (also referred to as acontroller or a controller IC) through a connection portion such as aflexible printed circuit (FPC).

In FIG. 29A, the scan line driver circuit 702, the scan line drivercircuit 703, and the signal line driver circuit 704 are formed over thesubstrate 700 where the pixel portion 701 is formed. Accordingly, thenumber of components which are provided outside, such as a drivercircuit, can be reduced, so that a reduction in cost can be achieved.Furthermore, if the driver circuit is provided outside the substrate700, wirings would need to be extended and the number of wiringconnections would increase. When the driver circuit is provided over thesubstrate 700, the number of wiring connections can be reduced.Consequently, an improvement in reliability or yield can be achieved.

[Liquid Crystal Display Device]

FIG. 29B illustrates an example of a circuit configuration of the pixel.Here, a pixel circuit which is applicable to a pixel of a VA liquidcrystal display device is illustrated as an example.

This pixel circuit can be applied to a structure in which one pixelincludes a plurality of pixel electrode layers. The pixel electrodelayers are connected to different transistors, and the transistors canbe driven with different gate signals. Accordingly, signals applied toindividual pixel electrode layers in a multi-domain pixel can becontrolled independently.

A gate wiring 712 of a transistor 716 and a gate wiring 713 of atransistor 717 are separated so that different gate signals can besupplied thereto. In contrast, a data line 714 is shared by thetransistors 716 and 717. The transistor described in any of the aboveembodiments can be used as appropriate as each of the transistors 716and 717. Thus, a highly reliable liquid crystal display device can beprovided.

The shapes of a first pixel electrode layer electrically connected tothe transistor 716 and a second pixel electrode layer electricallyconnected to the transistor 717 are described. The first pixel electrodeand the second pixel electrode are separated. Shapes of the first pixelelectrode and the second pixel electrode are not especially limited. Forexample, the first pixel electrode may have a V-like shape.

A gate electrode of the transistor 716 is connected to the gate wiring712, and a gate electrode of the transistor 717 is connected to the gatewiring 713. When different gate signals are supplied to the gate wiring712 and the gate wiring 713, operation timings of the transistor 716 andthe transistor 717 can be varied. As a result, alignment of liquidcrystals can be controlled.

Furthermore, storage capacitors may be formed using a capacitor wiring710, gate insulating films functioning as dielectrics, and capacitorelectrodes electrically connected to the first pixel electrode layer andthe second pixel electrode layer.

The multi-domain pixel includes a first liquid crystal element 718 and asecond liquid crystal element 719. The first liquid crystal element 718includes the first pixel electrode layer, a counter electrode layer, anda liquid crystal layer therebetween. The second liquid crystal element719 includes the second pixel electrode layer, a counter electrodelayer, and a liquid crystal layer therebetween.

Note that a pixel circuit of the present invention is not limited tothat shown in FIG. 29B. For example, a switch, a resistor, a capacitor,a transistor, a sensor, a logic circuit, or the like may be added to thepixel circuit illustrated in FIG. 29B.

[Organic EL Display Device]

FIG. 29C illustrates another example of a circuit configuration of thepixel. Here, a pixel structure of a display device using an organic ELelement is shown.

In an organic EL element, by application of voltage to a light-emittingelement, electrons are injected from one of a pair of electrodes andholes are injected from the other of the pair of electrodes, into alayer containing a light-emitting organic compound; thus, current flows.The electrons and holes are recombined, and thus, the light-emittingorganic compound is excited. The light-emitting organic compound returnsto a ground state from the excited state, thereby emitting light. Owingto such a mechanism, this light-emitting element is referred to as acurrent-excitation light-emitting element.

FIG. 29C illustrates an applicable example of a pixel circuit. Here, onepixel includes two n-channel transistors. Note that a metal oxide filmof one embodiment of the present invention can be used for a channelformation region of the n-channel transistor. Further, digital timegrayscale driving can be employed for the pixel circuit.

The configuration of the applicable pixel circuit and operation of apixel employing digital time grayscale driving will be described.

A pixel 720 includes a switching transistor 721, a driver transistor722, a light-emitting element 724, and a capacitor 723. A gate electrodelayer of the switching transistor 721 is connected to a scan line 726, afirst electrode (one of a source electrode layer and a drain electrodelayer) of the switching transistor 721 is connected to a signal line725, and a second electrode (the other of the source electrode layer andthe drain electrode layer) of the switching transistor 721 is connectedto a gate electrode layer of the driver transistor 722. The gateelectrode layer of the driver transistor 722 is connected to a powersupply line 727 through the capacitor 723, a first electrode of thedriver transistor 722 is connected to the power supply line 727, and asecond electrode of the driver transistor 722 is connected to a firstelectrode (a pixel electrode) of the light-emitting element 724. Asecond electrode of the light-emitting element 724 corresponds to acommon electrode 728. The common electrode 728 is electrically connectedto a common potential line formed over the same substrate as the commonelectrode 728.

As the switching transistor 721 and the driver transistor 722, any ofthe transistors described in other embodiments can be used asappropriate. In this manner, a highly reliable organic EL display devicecan be provided.

The potential of the second electrode (the common electrode 728) of thelight-emitting element 724 is set to be a low power supply potential.Note that the low power supply potential is lower than a high powersupply potential supplied to the power supply line 727. For example, thelow power supply potential can be GND, 0 V, or the like. The high powersupply potential and the low power supply potential are set to be higherthan or equal to the forward threshold voltage of the light-emittingelement 724, and the difference between the potentials is applied to thelight-emitting element 724, whereby current is supplied to thelight-emitting element 724, leading to light emission. The forwardvoltage of the light-emitting element 724 refers to a voltage at which adesired luminance is obtained, and includes at least a forward thresholdvoltage.

Note that the gate capacitance of the driver transistor 722 may be usedas a substitute for the capacitor 723, so that the capacitor 723 can beomitted. The gate capacitance of the driver transistor 722 may be formedbetween the channel formation region and the gate electrode layer.

Next, a signal input to the driver transistor 722 will be described. Inthe case of a voltage-input voltage driving method, a video signal forsufficiently turning on or off the driver transistor 722 is input to thedriver transistor 722. In order for the driver transistor 722 to operatein a linear region, voltage higher than the voltage of the power supplyline 727 is applied to the gate electrode layer of the driver transistor722. Note that voltage higher than or equal to voltage which is the sumof power supply line voltage and the threshold voltage V_(th) of thedriver transistor 722 is applied to the signal line 725.

In the case of performing analog grayscale driving, a voltage higherthan or equal to a voltage which is the sum of the forward voltage ofthe light-emitting element 724 and the threshold voltage V_(t)h of thedriver transistor 722 is applied to the gate electrode layer of thedriver transistor 722. A video signal by which the driver transistor 722is operated in a saturation region is input, so that current is suppliedto the light-emitting element 724. In order for the driver transistor722 to operate in a saturation region, the potential of the power supplyline 727 is set higher than the gate potential of the driver transistor722. When an analog video signal is used, it is possible to supplycurrent to the light-emitting element 724 in accordance with the videosignal and perform analog grayscale driving.

Note that the configuration of the pixel circuit of the presentinvention is not limited to that shown in FIG. 29C. For example, aswitch, a resistor, a capacitor, a sensor, a transistor, a logiccircuit, or the like may be added to the pixel circuit illustrated inFIG. 29C.

In the case where the transistor shown in the above embodiments is usedfor the circuit shown in FIGS. 29A to 29C, the source electrode (thefirst electrode) is electrically connected to the low potential side andthe drain electrode (the second electrode) is electrically connected tothe high potential side. Furthermore, the potential of the first gateelectrode may be controlled by a control circuit or the like and thepotential described above as an example, e.g., a potential lower thanthe potential applied to the source electrode, may be input to thesecond gate electrode through a wiring that is not illustrated.

For example, in this specification and the like, for example, a displayelement, a display device which is a device including a display element,a light-emitting element, and a light-emitting device which is a deviceincluding a light-emitting element can employ a variety of modes or caninclude a variety of elements. The display element, the display device,the light-emitting element, or the light-emitting device includes atleast one of an electroluminescence (EL) element (e.g., an EL elementincluding organic and inorganic materials, an organic EL element, or aninorganic EL element), an LED (e.g., a white LED, a red LED, a greenLED, or a blue LED), a transistor (a transistor that emits lightdepending on current), an electron emitter, a liquid crystal element,electronic ink, an electrophoretic element, a grating light valve (GLV),a plasma display panel (PDP), a display element using micro electromechanical systems (MEMS), a digital micromirror device (DMD), a digitalmicro shutter (DMS), MIRASOL (registered trademark), an interferometricmodulator display (IMOD) element, a MEMS shutter display element, anoptical-interference-type MEMS display element, an electrowettingelement, a piezoelectric ceramic display, a display element including acarbon nanotube, and the like. Other than the above, a display mediumwhose contrast, luminance, reflectance, transmittance, or the like ischanged by an electrical or magnetic effect may be included. Note thatexamples of a display device including an EL element include an ELdisplay. Examples of a display device including an electron emitterinclude a field emission display (FED) and an SED-type flat paneldisplay (SED: surface-conduction electron-emitter display). Examples ofa display device including a liquid crystal element include a liquidcrystal display (e.g., a transmissive liquid crystal display, atransflective liquid crystal display, a reflective liquid crystaldisplay, a direct-view liquid crystal display, or a projection liquidcrystal display). Examples of a display device including electronic ink,Electronic Liquid Powder (registered trademark), or an electrophoreticelement include electronic paper. In the case of a transflective liquidcrystal display or a reflective liquid crystal display, some or all ofpixel electrodes function as reflective electrodes. For example, some orall of pixel electrodes are formed to contain aluminum, silver, or thelike. In such a case, a memory circuit such as an SRAM can be providedunder the reflective electrodes, leading to lower power consumption.Note that in the case of using an LED, graphene or graphite may beprovided under an electrode or a nitride semiconductor of the LED.Graphene or graphite may be a multilayer film in which a plurality oflayers are stacked. As described above, provision of graphene orgraphite enables easy formation of a nitride semiconductor thereover,such as an n-type GaN semiconductor layer including crystals.Furthermore, a p-type GaN semiconductor layer including crystals or thelike can be provided thereover, and thus the LED can be formed. Notethat an MN layer may be provided between the n-type GaN semiconductorlayer including crystals and graphene or graphite. The GaN semiconductorlayers included in the LED may be formed by MOCVD. Note that when thegraphene is provided, the GaN semiconductor layers included in the LEDcan also be formed by a sputtering method.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

Embodiment 7

In this embodiment, a structure of an oxide semiconductor film isdescribed.

<Structure of Oxide Semiconductor>

A structure of an oxide semiconductor is described below.

An oxide semiconductor is classified into a single crystal oxidesemiconductor and a non-single-crystal oxide semiconductor. Examples ofa non-single-crystal oxide semiconductor include a c-axis alignedcrystalline oxide semiconductor (CAAC-OS), a polycrystalline oxidesemiconductor, a microcrystalline oxide semiconductor, and an amorphousoxide semiconductor.

From another perspective, an oxide semiconductor is classified into anamorphous oxide semiconductor and a crystalline oxide semiconductor.Examples of a crystalline oxide semiconductor include a single crystaloxide semiconductor, a CAAC-OS, a polycrystalline oxide semiconductor,and a microcrystalline oxide semiconductor.

<CAAC-OS>

First, a CAAC-OS is described. Note that a CAAC-OS can be referred to asan oxide semiconductor including c-axis aligned nanocrystals (CANC).

A CAAC-OS is one of oxide semiconductors having a plurality of c-axisaligned crystal parts (also referred to as pellets).

In a combined analysis image (also referred to as a high-resolution TEMimage) of a bright-field image and a diffraction pattern of a CAAC-OS,which is obtained using a transmission electron microscope (TEM), aplurality of pellets can be observed. However, in the high-resolutionTEM image, a boundary between pellets, that is, a grain boundary is notclearly observed. Thus, in the CAAC-OS, a reduction in electron mobilitydue to the grain boundary is less likely to occur.

A CAAC-OS observed with TEM is described below. FIG. 30A shows ahigh-resolution TEM image of a cross section of the CAAC-OS which isobserved from a direction substantially parallel to the sample surface.The high-resolution TEM image is obtained with a spherical aberrationcorrector function. The high-resolution TEM image obtained with aspherical aberration corrector function is particularly referred to as aCs-corrected high-resolution TEM image. The Cs-corrected high-resolutionTEM image can be obtained with, for example, an atomic resolutionanalytical electron microscope JEM-ARM200F manufactured by JEOL Ltd.

FIG. 30B is an enlarged Cs-corrected high-resolution TEM image of aregion (1) in FIG. 30A. FIG. 30B shows that metal atoms are arranged ina layered manner in a pellet. Each metal atom layer has a configurationreflecting unevenness of a surface over which the CAAC-OS is formed(hereinafter, the surface is referred to as a formation surface) or atop surface of the CAAC-OS, and is arranged parallel to the formationsurface or the top surface of the CAAC-OS.

As shown in FIG. 30B, the CAAC-OS has a characteristic atomicarrangement. The characteristic atomic arrangement is denoted by anauxiliary line in FIG. 30C. FIGS. 30B and 30C prove that the size of apellet is approximately 1 nm to 3 nm, and the size of a space caused bytilt of the pellets is approximately 0.8 nm. Therefore, the pellet canalso be referred to as a nanocrystal (nc).

Here, according to the Cs-corrected high-resolution TEM images, theschematic arrangement of pellets 5100 of a CAAC-OS over a substrate 5120is illustrated by such a structure in which bricks or blocks are stacked(see FIG. 30D). The part in which the pellets are tilted as observed inFIG. 30C corresponds to a region 5161 shown in FIG. 30D.

FIG. 31A shows a Cs-corrected high-resolution TEM image of a plane ofthe CAAC-OS observed from a direction substantially perpendicular to thesample surface. FIGS. 31B, 31C, and 31D are enlarged Cs-correctedhigh-resolution TEM images of regions (1), (2), and (3) in FIG. 31A,respectively. FIGS. 31B, 31C, and 31D indicate that metal atoms arearranged in a triangular, quadrangular, or hexagonal configuration in apellet. However, there is no regularity of arrangement of metal atomsbetween different pellets.

Next, a CAAC-OS analyzed by X-ray diffraction (XRD) is described. Forexample, when the structure of a CAAC-OS including an InGaZnO₄ crystalis analyzed by an out-of-plane method, a peak appears at a diffractionangle (2θ) of around 31° as shown in FIG. 32A. This peak is derived fromthe (009) plane of the InGaZnO₄ crystal, which indicates that crystalsin the CAAC-OS have c-axis alignment, and that the c-axes are aligned ina direction substantially perpendicular to the formation surface or thetop surface of the CAAC-OS.

Note that in structural analysis of the CAAC-OS by an out-of-planemethod, another peak may appear when 2θ is around 36°, in addition tothe peak at 2θ of around 31°. The peak at 2θ of around 36° indicatesthat a crystal having no c-axis alignment is included in part of theCAAC-OS. It is preferable that in the CAAC-OS analyzed by anout-of-plane method, a peak appear when 2θ is around 31° and that a peaknot appear when 2θ is around 36°.

On the other hand, in structural analysis of the CAAC-OS by an in-planemethod in which an X-ray is incident on a sample in a directionsubstantially perpendicular to the c-axis, a peak appears when 2θ isaround 56°. This peak is attributed to the (110) plane of the InGaZnO₄crystal. In the case of the CAAC-OS, when analysis (ϕ scan) is performedwith 2θ fixed at around 56° and with the sample rotated using a normalvector of the sample surface as an axis (ϕ axis), as shown in FIG. 32B,a peak is not clearly observed. In contrast, in the case of a singlecrystal oxide semiconductor of InGaZnO₄, when ϕ scan is performed with28 fixed at around 56°, as shown in FIG. 32C, six peaks which arederived from crystal planes equivalent to the (110) plane are observed.Accordingly, the structural analysis using XRD shows that the directionsof a-axes and b-axes are irregularly oriented in the CAAC-OS.

Next, a CAAC-OS analyzed by electron diffraction is described. Forexample, when an electron beam with a probe diameter of 300 nm isincident on a CAAC-OS including an InGaZnO₄ crystal in a directionparallel to the sample surface, a diffraction pattern (also referred toas a selected-area transmission electron diffraction pattern) shown inFIG. 33A can be obtained. In this diffraction pattern, spots derivedfrom the (009) plane of an InGaZnO₄ crystal are included. Thus, theelectron diffraction also indicates that pellets included in the CAAC-OShave c-axis alignment and that the c-axes are aligned in a directionsubstantially perpendicular to the formation surface or the top surfaceof the CAAC-OS. Meanwhile, FIG. 33B shows a diffraction pattern obtainedin such a manner that an electron beam with a probe diameter of 300 nmis incident on the same sample in a direction perpendicular to thesample surface. As shown in FIG. 33B, a ring-like diffraction pattern isobserved. Thus, the electron diffraction also indicates that the a-axesand b-axes of the pellets included in the CAAC-OS do not have regularalignment. The first ring in FIG. 33B is considered to be derived fromthe (010) plane, the (100) plane, and the like of the InGaZnO₄ crystal.The second ring in FIG. 33B is considered to be derived from the (110)plane and the like.

Moreover, the CAAC-OS is an oxide semiconductor having a low density ofdefect states. Defects in the oxide semiconductor are, for example, adefect due to impurity and oxygen vacancies. Therefore, the CAAC-OS canbe regarded as an oxide semiconductor with a low impurity concentration,or an oxide semiconductor having a small number of oxygen vacancies.

The impurity contained in the oxide semiconductor might serve as acarrier trap or serve as a carrier generation source. Furthermore,oxygen vacancies in the oxide semiconductor serve as carrier traps orserve as carrier generation sources when hydrogen is captured therein.

Note that the impurity means an element other than the main componentsof the oxide semiconductor, such as hydrogen, carbon, silicon, or atransition metal element. For example, an element (specifically, siliconor the like) having higher strength of bonding to oxygen than a metalelement included in an oxide semiconductor extracts oxygen from theoxide semiconductor, which results in disorder of the atomic arrangementand reduced crystallinity of the oxide semiconductor. A heavy metal suchas iron or nickel, argon, carbon dioxide, or the like has a large atomicradius (or molecular radius), and thus disturbs the atomic arrangementof the oxide semiconductor and decreases crystallinity.

An oxide semiconductor having a low density of defect states (a smallnumber of oxygen vacancies) can have a low carrier density. Such anoxide semiconductor is referred to as a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. A CAAC-OShas a low impurity concentration and a low density of defect states.That is, a CAAC-OS is likely to be a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. Thus, atransistor including a CAAC-OS rarely has negative threshold voltage (israrely normally on). The highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor has few carrier traps. Anelectric charge trapped by the carrier traps in the oxide semiconductortakes a long time to be released. The trapped electric charge may behavelike a fixed electric charge. Thus, the transistor which includes theoxide semiconductor having a high impurity concentration and a highdensity of defect states might have unstable electrical characteristics.However, a transistor including a CAAC-OS has small variation inelectrical characteristics and high reliability.

Since the CAAC-OS has a low density of defect states, carriers generatedby light irradiation or the like are less likely to be trapped in defectstates. Therefore, in a transistor using the CAAC-OS, change inelectrical characteristics due to irradiation with visible light orultraviolet light is small.

<Microcrystalline Oxide Semiconductor>

Next, a microcrystalline oxide semiconductor is described.

A microcrystalline oxide semiconductor has a region in which a crystalpart is observed and a region in which a crystal part is not clearlyobserved in a high-resolution TEM image. In most cases, the size of acrystal part included in the microcrystalline oxide semiconductor isgreater than or equal to 1 nm and less than or equal to 100 nm, orgreater than or equal to 1 nm and less than or equal to 10 nm. An oxidesemiconductor including a nanocrystal (nc) that is a microcrystal with asize greater than or equal to 1 nm and less than or equal to 10 nm, or asize greater than or equal to 1 nm and less than or equal to 3 nm isspecifically referred to as a nanocrystalline oxide semiconductor(nc-OS). In a high-resolution TEM image of the nc-OS, for example, agrain boundary is not clearly observed in some cases. Note that there isa possibility that the origin of the nanocrystal is the same as that ofa pellet in a CAAC-OS. Therefore, a crystal part of the nc-OS may bereferred to as a pellet in the following description.

In the nc-OS, a microscopic region (for example, a region with a sizegreater than or equal to 1 nm and less than or equal to 10 nm, inparticular, a region with a size greater than or equal to 1 nm and lessthan or equal to 3 nm) has a periodic atomic arrangement. There is noregularity of crystal orientation between different pellets in thenc-OS. Thus, the orientation of the whole film is not ordered.Accordingly, the nc-OS cannot be distinguished from an amorphous oxidesemiconductor, depending on an analysis method. For example, when thenc-OS is subjected to structural analysis by an out-of-plane method withan XRD apparatus using an X-ray having a diameter larger than the sizeof a pellet, a peak which shows a crystal plane does not appear.Furthermore, a diffraction pattern like a halo pattern is observed whenthe nc-OS is subjected to electron diffraction using an electron beamwith a probe diameter (e.g., 50 nm or larger) that is larger than thesize of a pellet (the electron diffraction is also referred to asselected-area electron diffraction). Meanwhile, spots appear in ananobeam electron diffraction pattern of the nc-OS when an electron beamhaving a probe diameter close to or smaller than the size of a pellet isapplied. Moreover, in a nanobeam electron diffraction pattern of thenc-OS, regions with high luminance in a circular (ring) pattern areshown in some cases. Also in a nanobeam electron diffraction pattern ofthe nc-OS, a plurality of spots is shown in a ring-like region in somecases.

Since there is no regularity of crystal orientation between the pellets(nanocrystals) as mentioned above, the nc-OS can also be referred to asan oxide semiconductor including random aligned nanocrystals (RANC) oran oxide semiconductor including non-aligned nanocrystals (NANC).

The nc-OS is an oxide semiconductor that has high regularity as comparedwith an amorphous oxide semiconductor. Therefore, the nc-OS is likely tohave a lower density of defect states than an amorphous oxidesemiconductor. Note that there is no regularity of crystal orientationbetween different pellets in the nc-OS. Therefore, the nc-OS has ahigher density of defect states than the CAAC-OS.

<Amorphous Oxide Semiconductor>

Next, an amorphous oxide semiconductor is described.

The amorphous oxide semiconductor is an oxide semiconductor havingdisordered atomic arrangement and no crystal part and exemplified by anoxide semiconductor which exists in an amorphous state as quartz.

In a high-resolution TEM image of the amorphous oxide semiconductor,crystal parts cannot be found.

When the amorphous oxide semiconductor is subjected to structuralanalysis by an out-of-plane method with an XRD apparatus, a peak whichshows a crystal plane does not appear. A halo pattern is observed whenthe amorphous oxide semiconductor is subjected to electron diffraction.Furthermore, a spot is not observed and only a halo pattern appears whenthe amorphous oxide semiconductor is subjected to nanobeam electrondiffraction.

There are various understandings of an amorphous structure. For example,a structure whose atomic arrangement does not have ordering at all iscalled a completely amorphous structure. Meanwhile, a structure whichdoes not have long-range ordering but might have ordering in a rangefrom an atom to the nearest neighbor atoms or to the second-nearestneighbor atoms is also called an amorphous structure. Therefore, thestrictest definition does not permit an oxide semiconductor to be calledan amorphous oxide semiconductor as long as even a negligible degree ofordering is present in an atomic arrangement. At least an oxidesemiconductor having long-term ordering cannot be called an amorphousoxide semiconductor. Accordingly, because of the presence of crystalpart, for example, a CAAC-OS and an nc-OS cannot be called an amorphousoxide semiconductor or a completely amorphous oxide semiconductor.

<Amorphous-Like Oxide Semiconductor>

Note that an oxide semiconductor may have a structure intermediatebetween the nc-OS and the amorphous oxide semiconductor. The oxidesemiconductor having such a structure is specifically referred to as anamorphous-like oxide semiconductor (a-like OS).

In a high-resolution TEM image of the a-like OS, a void may be observed.Furthermore, in the high-resolution TEM image, there are a region wherea crystal part is clearly observed and a region where a crystal part isnot observed.

The a-like OS has an unstable structure because it contains a void. Toverify that an a-like OS has an unstable structure as compared with aCAAC-OS and an nc-OS, a change in structure caused by electronirradiation is described below.

An a-like OS (referred to as Sample A), an nc-OS (referred to as SampleB), and a CAAC-OS (referred to as Sample C) are prepared as samplessubjected to electron irradiation. Each of the samples is an In—Ga—Znoxide.

First, a high-resolution cross-sectional TEM image of each sample isobtained. The high-resolution cross-sectional TEM images show that allthe samples have crystal parts.

Note that which part is regarded as a crystal part is determined asfollows. It is known that a unit cell of an InGaZnO₄ crystal has astructure in which nine layers including three In—O layers and sixGa—Zn—O layers are stacked in the c-axis direction. The distance betweenthe adjacent layers is equivalent to the lattice spacing on the (009)plane (also referred to as d value). The value is calculated to be 0.29nm from crystal structural analysis. Accordingly, a portion where thelattice spacing between lattice fringes is greater than or equal to 0.28nm and less than or equal to 0.30 nm is regarded as a crystal part ofInGaZnO₄. Each of lattice fringes corresponds to the a-b plane of theInGaZnO₄ crystal.

FIG. 34 shows change in the average size of crystal parts (at 22 pointsto 45 points) in each sample. Note that the crystal part sizecorresponds to the length of a lattice fringe. FIG. 34 indicates thatthe crystal part size in the a-like OS increases with an increase in thecumulative electron dose. Specifically, as shown by (1) in FIG. 34, acrystal part of approximately 1.2 nm (also referred to as an initialnucleus) at the start of TEM observation grows to a size ofapproximately 2.6 nm at a cumulative electron dose of 4.2×10⁸ e⁻/nm². Incontrast, the crystal part size in the nc-OS and the CAAC-OS showslittle change from the start of electron irradiation to a cumulativeelectron dose of 4.2×10⁸ e⁻/nm². Specifically, as shown by (2) and (3)in FIG. 34, the average crystal sizes in an nc-OS and a CAAC-OS areapproximately 1.4 nm and approximately 2.1 nm, respectively, regardlessof the cumulative electron dose.

In this manner, growth of the crystal part in the a-like OS is inducedby electron irradiation. In contrast, in the nc-OS and the CAAC-OS,growth of the crystal part is hardly induced by electron irradiation.Therefore, the a-like OS has an unstable structure as compared with thenc-OS and the CAAC-OS.

The a-like OS has a lower density than the nc-OS and the CAAC-OS becauseit contains a void. Specifically, the density of the a-like OS is higherthan or equal to 78.6% and lower than 92.3% of the density of the singlecrystal oxide semiconductor having the same composition. The density ofeach of the nc-OS and the CAAC-OS is higher than or equal to 92.3% andlower than 100% of the density of the single crystal oxide semiconductorhaving the same composition. Note that it is difficult to deposit anoxide semiconductor having a density of lower than 78% of the density ofthe single crystal oxide semiconductor.

For example, in the case of an oxide semiconductor having an atomicratio of In:Ga:Zn=1:1:1, the density of single crystal InGaZnO₄ with arhombohedral crystal structure is 6.357 g/cm³. Accordingly, in the caseof the oxide semiconductor having an atomic ratio of In:Ga:Zn=1:1:1, thedensity of the a-like OS is higher than or equal to 5.0 g/cm³ and lowerthan 5.9 g/cm³. For example, in the case of the oxide semiconductorhaving an atomic ratio of In:Ga:Zn=1:1:1, the density of each of thenc-OS and the CAAC-OS is higher than or equal to 5.9 g/cm³ and lowerthan 6.3 g/cm³.

Note that there is a possibility that an oxide semiconductor having acertain composition cannot exist in a single crystal structure. In thatcase, single crystal oxide semiconductors with different compositionsare combined at an adequate ratio, which makes it possible to calculatedensity equivalent to that of a single crystal oxide semiconductor withthe desired composition. The density of a single crystal oxidesemiconductor having the desired composition can be calculated using aweighted average according to the combination ratio of the singlecrystal oxide semiconductors with different compositions. Note that itis preferable to use as few kinds of single crystal oxide semiconductorsas possible to calculate the density.

As described above, oxide semiconductors have various structures andvarious properties. Note that an oxide semiconductor may be a stackedlayer including two or more films of an amorphous oxide semiconductor,an a-like OS, a microcrystalline oxide semiconductor, and a CAAC-OS, forexample

<Deposition Model>

Examples of deposition models of a CAAC-OS and an nc-OS are describedbelow.

FIG. 35A is a schematic view of the inside of a deposition chamber wherea CAAC-OS is deposited by a sputtering method.

A target 5130 is attached to a backing plate. A plurality of magnets isprovided to face the target 5130 with the backing plate positionedtherebetween. The plurality of magnets generates a magnetic field. Asputtering method in which the disposition rate is increased byutilizing a magnetic field of magnets is referred to as a magnetronsputtering method.

The substrate 5120 is placed to face the target 5130, and the distance d(also referred to as a target-substrate distance (T-S distance)) isgreater than or equal to 0.01 m and less than or equal to 1 m,preferably greater than or equal to 0.02 m and less than or equal to 0.5m. The deposition chamber is mostly filled with a deposition gas (e.g.,an oxygen gas, an argon gas, or a mixed gas containing oxygen at 5 vol %or higher) and the pressure in the deposition chamber is controlled tobe higher than or equal to 0.01 Pa and lower than or equal to 100 Pa,preferably higher than or equal to 0.1 Pa and lower than or equal to 10Pa. Here, discharge starts by application of a voltage at a certainvalue or higher to the target 5130, and plasma is observed. The magneticfield forms a high-density plasma region in the vicinity of the target5130. In the high-density plasma region, the deposition gas is ionized,so that an ion 5101 is generated. Examples of the ion 5101 include anoxygen cation (O⁺) and an argon cation (Ar⁺).

Here, the target 5130 has a polycrystalline structure which includes aplurality of crystal grains and in which a cleavage plane exists in atleast one crystal grain. FIG. 36A shows a structure of an InGaZnO₄crystal included in the target 5130 as an example Note that FIG. 36Ashows a structure of the case where the InGaZnO₄ crystal is observedfrom a direction parallel to the b-axis. FIG. 36A indicates that oxygenatoms in a Ga—Zn—O layer are positioned close to those in an adjacentGa—Zn—O layer. The oxygen atoms have negative charge, whereby repulsiveforce is generated between the two adjacent Ga—Zn—O layers. As a result,the InGaZnO₄ crystal has a cleavage plane between the two adjacentGa—Zn—O layers.

The ion 5101 generated in the high-density plasma region is acceleratedtoward the target 5130 side by an electric field, and then collides withthe target 5130. At this time, a pellet 5100 a and a pellet 5100 b whichare flat-plate-like (pellet-like) sputtered particles are separated andsputtered from the cleavage plane. Note that structures of the pellet5100 a and the pellet 5100 b may be distorted by an impact of collisionof the ion 5101.

The pellet 5100 a is a flat-plate-like (pellet-like) sputtered particlehaving a triangle plane, e.g., regular triangle plane. The pellet 5100 bis a flat-plate-like (pellet-like) sputtered particle having a hexagonplane, e.g., regular hexagon plane. Note that flat-plate-like(pellet-like) sputtered particles such as the pellet 5100 a and thepellet 5100 b are collectively called pellets 5100. The shape of a flatplane of the pellet 5100 is not limited to a triangle or a hexagon. Forexample, the flat plane may have a shape formed by combining two or moretriangles. For example, a quadrangle (e.g., rhombus) may be formed bycombining two triangles (e.g., regular triangles).

The thickness of the pellet 5100 is determined depending on the kind ofdeposition gas and the like. The thicknesses of the pellets 5100 arepreferably uniform; the reason for this is described later. In addition,the sputtered particle preferably has a pellet shape with a smallthickness as compared to a dice shape with a large thickness. Forexample, the thickness of the pellet 5100 is greater than or equal to0.4 nm and less than or equal to 1 nm, preferably greater than or equalto 0.6 nm and less than or equal to 0.8 nm. In addition, for example,the width of the pellet 5100 is greater than or equal to 1 nm and lessthan or equal to 3 nm, preferably greater than or equal to 1.2 nm andless than or equal to 2.5 nm. The pellet 5100 corresponds to the initialnucleus in the description of (1) in FIG. 34. For example, when the ion5101 collides with the target 5130 including an In—Ga—Zn oxide, thepellet 5100 that includes three layers of a Ga—Zn—O layer, an In—Olayer, and a Ga—Zn—O layer as shown in FIG. 36B is separated. Note thatFIG. 36C shows the structure of the separated pellet 5100 which isobserved from a direction parallel to the c-axis. The pellet 5100 has ananometer-sized sandwich structure including two Ga—Zn—O layers (piecesof bread) and an In—O layer (filling).

The pellet 5100 may receive a charge when passing through the plasma, sothat side surfaces thereof are negatively or positively charged. In thepellet 5100, for example, an oxygen atom positioned on its side surfacemay be negatively charged. When the side surfaces are charged with thesame polarity, charges repel each other, and accordingly, the pellet5100 can maintain a flat-plate (pellet) shape. In the case where aCAAC-OS is an In—Ga—Zn oxide, there is a possibility that an oxygen atombonded to an indium atom is negatively charged. There is anotherpossibility that an oxygen atom bonded to an indium atom, a galliumatom, or a zinc atom is negatively charged. In addition, the pellet 5100may grow by being bonded with an indium atom, a gallium atom, a zincatom, an oxygen atom, or the like when passing through plasma. Adifference in size between (2) and (1) in FIG. 34 corresponds to theamount of growth in plasma. Here, in the case where the temperature ofthe substrate 5120 is at around room temperature, the pellet 5100 on thesubstrate 5120 hardly grows; thus, an nc-OS is formed (see FIG. 35B). Annc-OS can be deposited when the substrate 5120 has a large size becausethe deposition of an nc-OS can be carried out at room temperature. Notethat in order that the pellet 5100 grows in plasma, it is effective toincrease deposition power in sputtering. High deposition power canstabilize the structure of the pellet 5100.

As shown in FIGS. 35A and 35B, the pellet 5100 flies like a kite inplasma and flutters up to the substrate 5120. Since the pellets 5100 arecharged, when the pellet 5100 gets close to a region where anotherpellet 5100 has already been deposited, repulsion is generated. Here,above the substrate 5120, a magnetic field in a direction parallel tothe top surface of the substrate 5120 (also referred to as a horizontalmagnetic field) is generated. A potential difference is given betweenthe substrate 5120 and the target 5130, and accordingly, current flowsfrom the substrate 5120 toward the target 5130. Thus, the pellet 5100 isgiven a force (Lorentz force) on the top surface of the substrate 5120by an effect of the magnetic field and the current. This is explainablewith Fleming's left-hand rule.

The mass of the pellet 5100 is larger than that of an atom. Therefore,to move the pellet 5100 over the top surface of the substrate 5120, itis important to apply some force to the pellet 5100 from the outside.One kind of the force may be force which is generated by the action of amagnetic field and current. In order to apply a sufficient force to thepellet 5100 so that the pellet 5100 moves over a top surface of thesubstrate 5120, it is preferable to provide, on the top surface, aregion where the magnetic field in a direction parallel to the topsurface of the substrate 5120 is 10 G or higher, preferably 20 G orhigher, further preferably 30 G or higher, still further preferably 50 Gor higher. Alternatively, it is preferable to provide, on the topsurface, a region where the magnetic field in a direction parallel tothe top surface of the substrate 5120 is 1.5 times or higher, preferablytwice or higher, further preferably 3 times or higher, still furtherpreferably 5 times or higher as high as the magnetic field in adirection perpendicular to the top surface of the substrate 5120.

At this time, the magnets and the substrate 5120 are moved or rotatedrelatively, whereby the direction of the horizontal magnetic field onthe top surface of the substrate 5120 continues to change. Therefore,the pellet 5100 can be moved in various directions on the top surface ofthe substrate 5120 by receiving forces in various directions.

Furthermore, as shown in FIG. 35A, when the substrate 5120 is heated,resistance between the pellet 5100 and the substrate 5120 due tofriction or the like is low. As a result, the pellet 5100 glides abovethe top surface of the substrate 5120. The glide of the pellet 5100 iscaused in a state where its flat plane faces the substrate 5120. Then,when the pellet 5100 reaches the side surface of another pellet 5100that has been already deposited, the side surfaces of the pellets 5100are bonded. At this time, the oxygen atom on the side surface of thepellet 5100 is released. With the released oxygen atom, oxygen vacanciesin a CAAC-OS might be filled; thus, the CAAC-OS has a low density ofdefect states. Note that the temperature of the top surface of thesubstrate 5120 is, for example, higher than or equal to 100° C. andlower than 500° C., higher than or equal to 150° C. and lower than 450°C., or higher than or equal to 170° C. and lower than 400° C. Hence,even when the substrate 5120 has a large size, it is possible to deposita CAAC-OS.

Furthermore, the pellet 5100 is heated on the substrate 5120, wherebyatoms are rearranged, and the structure distortion caused by thecollision of the ion 5101 can be reduced. The pellet 5100 whosestructure distortion is reduced is substantially single crystal. Evenwhen the pellets 5100 are heated after being bonded, expansion andcontraction of the pellet 5100 itself hardly occur, which is caused byturning the pellet 5100 into substantially single crystal. Thus,formation of defects such as a grain boundary due to expansion of aspace between the pellets 5100 can be prevented, and accordingly,generation of crevasses can be prevented.

The CAAC-OS does not have a structure like a board of a single crystaloxide semiconductor but has arrangement with a group of pellets 5100(nanocrystals) like stacked bricks or blocks. Furthermore, a grainboundary does not exist between the pellets 5100. Therefore, even whendeformation such as shrink occurs in the CAAC-OS owing to heating duringdeposition, heating or bending after deposition, it is possible torelieve local stress or release distortion. Therefore, this structure issuitable for a flexible semiconductor device. Note that the nc-OS hasarrangement in which pellets 5100 (nanocrystals) are randomly stacked.

When the target 5130 is sputtered with the ion 5101, in addition to thepellets 5100, zinc oxide or the like may be separated. The zinc oxide islighter than the pellet 5100 and thus reaches the top surface of thesubstrate 5120 before the pellet 5100. As a result, the zinc oxide formsa zinc oxide layer 5102 with a thickness greater than or equal to 0.1 nmand less than or equal to 10 nm, greater than or equal to 0.2 nm andless than or equal to 5 nm, or greater than or equal to 0.5 nm and lessthan or equal to 2 nm. FIGS. 37A to 37D are schematic cross-sectionalviews.

As illustrated in FIG. 37A, a pellet 5105 a and a pellet 5105 b aredeposited over the zinc oxide layer 5102. Here, side surfaces of thepellet 5105 a and the pellet 5105 b are in contact with each other. Inaddition, a pellet 5105 c is deposited over the pellet 5105 b, and thenglides over the pellet 5105 b. Furthermore, a plurality of particles5103 separated from the target together with the zinc oxide iscrystallized by heat from the substrate 5120 to form a region 5105 a 1on another side surface of the pellet 5105 a. Note that the plurality ofparticles 5103 may contain oxygen, zinc, indium, gallium, or the like.

Then, as illustrated in FIG. 37B, the region 5105 a 1 grows to part ofthe pellet 5105 a to form a pellet 5105 a 2. In addition, a side surfaceof the pellet 5105 c is in contact with another side surface of thepellet 5105 b.

Next, as illustrated in FIG. 37C, a pellet 5105 d is deposited over thepellet 5105 a 2 and the pellet 5105 b, and then glides over the pellet5105 a 2 and the pellet 5105 b. Furthermore, a pellet 5105 e glidestoward another side surface of the pellet 5105 c over the zinc oxidelayer 5102.

Then, as illustrated in FIG. 37D, the pellet 5105 d is placed so that aside surface of the pellet 5105 d is in contact with a side surface ofthe pellet 5105 a 2. Furthermore, a side surface of the pellet 5105 e isin contact with another side surface of the pellet 5105 c. A pluralityof particles 5103 separated from the target 5130 together with the zincoxide is crystallized by heat from the substrate 5120 to form a region5105 d 1 on another side surface of the pellet 5105 d.

As described above, deposited pellets are placed to be in contact witheach other and then growth is caused at side surfaces of the pellets,whereby a CAAC-OS is formed over the substrate 5120. Therefore, eachpellet of the CAAC-OS is larger than that of the nc-OS. A difference insize between (3) and (2) in FIG. 34 corresponds to the amount of growthafter deposition.

When spaces between pellets are extremely small, the pellets may form alarge pellet. The large pellet has a single crystal structure. Forexample, the size of the pellet may be greater than or equal to 10 nmand less than or equal to 200 nm, greater than or equal to 15 nm andless than or equal to 100 nm, or greater than or equal to 20 nm and lessthan or equal to 50 nm, when seen from the above. In this case, in anoxide semiconductor used for a minute transistor, a channel formationregion might be fit inside the large pellet. That is, the region havinga single crystal structure can be used as the channel formation region.Furthermore, when the size of the pellet is increased, the region havinga single crystal structure can be used as the channel formation region,the source region, and the drain region of the transistor.

In this manner, when the channel formation region or the like of thetransistor is formed in a region having a single crystal structure, thefrequency characteristics of the transistor can be increased in somecases.

As shown in such a model, the pellets 5100 are considered to bedeposited on the substrate 5120. Thus, a CAAC-OS can be deposited evenwhen a formation surface does not have a crystal structure; therefore, agrowth mechanism in this case is different from epitaxial growth. Inaddition, laser crystallization is not needed for formation of aCAAC-OS, and a uniform film can be formed even over a large-sized glasssubstrate or the like. For example, even when the top surface (formationsurface) of the substrate 5120 has an amorphous structure (e.g., the topsurface is formed of amorphous silicon oxide), a CAAC-OS can be formed.

In addition, it is found that in formation of the CAAC-OS, the pellets5100 are arranged in accordance with the top surface shape of thesubstrate 5120 that is the formation surface even when the formationsurface has unevenness. For example, in the case where the top surfaceof the substrate 5120 is flat at the atomic level, the pellets 5100 arearranged so that flat planes parallel to the a-b plane face downwards.In the case where the thicknesses of the pellets 5100 are uniform, alayer with a uniform thickness, flatness, and high crystallinity isformed. By stacking n layers (n is a natural number), the CAAC-OS can beobtained.

In the case where the top surface of the substrate 5120 has unevenness,a CAAC-OS in which n layers (n is a natural number) in each of which thepellets 5100 are arranged along the unevenness are stacked is formed.Since the substrate 5120 has unevenness, a gap is easily generatedbetween the pellets 5100 in the CAAC-OS in some cases. Note that, evenin such a case, owing to intermolecular force, the pellets 5100 arearranged so that a gap between the pellets is as small as possible evenon the unevenness surface. Therefore, even when the formation surfacehas unevenness, a CAAC-OS with high crystallinity can be obtained.

Since a CAAC-OS is deposited in accordance with such a model, thesputtered particle preferably has a pellet shape with a small thickness.Note that when the sputtered particles have a dice shape with a largethickness, planes facing the substrate 5120 vary; thus, the thicknessesand orientations of the crystals cannot be uniform in some cases.

According to the deposition model described above, a CAAC-OS with highcrystallinity can be formed even on a formation surface with anamorphous structure.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments. CLEMBODIMENT 8

[Electronic Device]

In this embodiment, examples of an electronic device to which thedisplay device of one embodiment of the present invention can be appliedwill be described with reference to FIGS. 38A to 38F and FIGS. 39A to39D.

Examples of an electronic device including the display device includetelevision sets (also referred to as televisions or televisionreceivers), monitors of computers or the like, cameras such as digitalcameras or digital video cameras, digital photo frames, mobile phones(also referred to as cellular phones or mobile phone devices), portablegame machines, portable information terminals, audio reproducingdevices, and large game machines such as pachinko machines. Specificexamples of these electronic devices are illustrated in FIGS. 38A to 38Fand FIGS. 39A to 39D.

FIG. 38A illustrates a portable game machine including a housing 7101, ahousing 7102, a display portion 7103, a display portion 7104, amicrophone 7105, speakers 7106, an operation key 7107, a stylus 7108,and the like. The display device according to one embodiment of thepresent invention can be used for the display portion 7103 or thedisplay portion 7104. When the display device according to oneembodiment of the present invention is used as the display portion 7103or 7104, it is possible to provide a user-friendly portable game machinewith quality that hardly deteriorates. Although the portable gamemachine illustrated in FIG. 38A includes two display portions, thedisplay portion 7103 and the display portion 7104, the number of displayportions included in the portable game machine is not limited to two.

FIG. 38B illustrates a smart watch, which includes a housing 7302, adisplay portion 7304, operation buttons 7311 and 7312, a connectionterminal 7313, a band 7321, a clasp 7322, and the like. The displaydevice or touch panel of one embodiment of the present invention can beused for the display portion 7304.

FIG. 38C illustrates a portable information terminal, which includes adisplay portion 7502 incorporated in a housing 7501, operation buttons7503, an external connection port 7504, a speaker 7505, a microphone7506, and the like. The display device of one embodiment of the presentinvention can be used for the display portion 7502.

FIG. 38D illustrates a video camera, which includes a first housing7701, a second housing 7702, a display portion 7703, operation keys7704, a lens 7705, a joint 7706, and the like. The operation keys 7704and the lens 7705 are provided for the first housing 7701, and thedisplay portion 7703 is provided for the second housing 7702. The firsthousing 7701 and the second housing 7702 are connected to each otherwith the joint 7706, and the angle between the first housing 7701 andthe second housing 7702 can be changed with the joint 7706. Imagesdisplayed on the display portion 7703 may be switched in accordance withthe angle at the joint 7706 between the first housing 7701 and thesecond housing 7702. The imaging device in one embodiment of the presentinvention can be provided in a focus position of the lens 7705. Thedisplay device of one embodiment of the present invention can be usedfor the image display portion 7703.

FIG. 38E illustrates a curved display including a display portion 7802incorporated in a housing 7801, an operation button 7803, a speaker7804, and the like. The display device of one embodiment of the presentinvention can be used for the display portion 7802.

FIG. 38F illustrates a digital signage including a display portion 7922provided on a utility pole 7921. The display device of one embodiment ofthe present invention can be used for the display portion 7922.

FIG. 39A illustrates a notebook personal computer, which includes ahousing 8121, a display portion 8122, a keyboard 8123, a pointing device8124, and the like. The display device of one embodiment of the presentinvention can be used for the display portion 8122.

FIG. 39B is an external view of an automobile 9700. FIG. 39C illustratesa driver's seat of the automobile 9700. The automobile 9700 includes acar body 9701, wheels 9702, a dashboard 9703, lights 9704, and the like.The display device or input/output device of one embodiment of thepresent invention can be used in a display portion or the like of theautomobile 9700. For example, the display device, input/output device,or touch panel of one embodiment of the present invention can be used indisplay portions 9710 to 9715 illustrated in FIG. 39C.

The display portion 9710 and the display portion 9711 are each a displaydevice or an input/output device provided in an automobile windshield.The display device or input/output device of one embodiment of thepresent invention can be a see-through display device or input/outputdevice, through which the opposite side can be seen, using alight-transmitting conductive material for its electrodes. Such asee-through display device or input/output device does not hinderdriver's vision during driving the automobile 9700. Thus, the displaydevice or input/output device of one embodiment of the present inventioncan be provided in the windshield of the automobile 9700. Note that inthe case where a transistor or the like for driving the display deviceor input/output device is provided in the display device or input/outputdevice, a transistor having a light-transmitting property, such as anorganic transistor using an organic semiconductor material or atransistor using an oxide semiconductor, is preferably used.

The display portion 9712 is a display device provided on a pillarportion. For example, an image taken by an imaging unit provided in thecar body is displayed on the display portion 9712, whereby the viewhindered by the pillar portion can be compensated. The display portion9713 is a display device provided on the dashboard. For example, animage taken by an imaging unit provided in the car body is displayed onthe display portion 9713, whereby the view hindered by the dashboard canbe compensated. That is, by displaying an image taken by an imaging unitprovided on the outside of the automobile, blind areas can be eliminatedand safety can be increased. Displaying an image to compensate for thearea which a driver cannot see, makes it possible for the driver toconfirm safety easily and comfortably.

FIG. 39D illustrates the inside of a car in which bench seats are usedfor a driver seat and a front passenger seat. A display portion 9721 isa display device provided in a door portion. For example, an image takenby an imaging unit provided in the car body is displayed on the displayportion 9721, whereby the view hindered by the door can be compensated.A display portion 9722 is a display device provided in a steering wheel.A display portion 9723 is a display device provided in the middle of aseating face of the bench seat. Note that the display device can be usedas a seat heater by providing the display device on the seating face orbackrest and by using heat generation of the display device as a heatsource.

The display portion 9714, the display portion 9715, and the displayportion 9722 can provide a variety of kinds of information such asnavigation data, a speedometer, a tachometer, a mileage, a fuel meter, agearshift indicator, and air-condition setting. The content, layout, orthe like of the display on the display portions can be changed freely bya user as appropriate. The information listed above can also bedisplayed on the display portions 9710 to 9713, 9721, and 9723. Thedisplay portions 9710 to 9715 and 9721 to 9723 can also be used aslighting devices. The display portions 9710 to 9715 and 9721 to 9723 canalso be used as heating devices.

A display portion including the display device of one embodiment of thepresent invention can be flat, in which case the display device does notnecessarily have a curved surface or flexibility.

Note that the structures, methods, and the like described in thisembodiment can be used as appropriate in combination with any of thestructures, methods, and the like described in the other embodiments.

REFERENCE NUMERALS

-   -   10: display device, 11: region, 12: region, 13: region, 14:        region, 18: light-blocking layer, 20: display panel, 21: display        region, 22: peripheral circuit, 23: protective film, 24: pixel,        30: groove portion, 36: electrode, 42: FPC, 50: transistor, 51:        transistor, 52: transistor, 53: transistor, 54: transistor, 55:        transistor, 61: capacitor, 63: capacitor, 70: light-emitting        element, 80: liquid crystal element, 90: input device, 91:        source line, 92: gate line, 100: substrate, 101: substrate, 103:        polarizing plate, 104: backlight, 110: insulating layer, 112:        insulating layer, 120: conductive layer, 130: insulating layer,        131: insulating layer, 140: semiconductor layer, 141: oxide        semiconductor layer, 142: oxide semiconductor layer, 143: oxide        semiconductor layer, 150: conductive layer, 160: conductive        layer, 165: insulating layer, 170: insulating layer, 180:        insulating layer, 190: conductive layer, 200: conductive layer,        220: conductive layer, 230: layer, 240: spacer, 250: EL layer,        260: conductive layer, 300: substrate, 301: substrate, 302:        protective substrate, 303: polarizing plate, 312: insulating        layer, 330: insulating layer, 360: coloring layer, 370: adhesive        layer, 371: adhesive layer, 372: adhesive layer, 373: adhesive        layer, 374: adhesive layer, 375: adhesive layer, 376: adhesive        layer, 380: conductive layer, 390: liquid crystal layer, 400:        conductive layer, 410: conductive layer, 411: conductive layer,        420: insulating layer, 430: conductive layer, 440: insulating        layer, 510: anisotropic conductive film, 520: conductive layer,        530: opening, 601: precursor, 602: precursor, 700: substrate,        701: pixel portion, 702: scan line driver circuit, 703: scan        line driver circuit, 704: signal line driver circuit, 710:        capacitor wiring, 712: gate wiring, 713: gate wiring, 714: data        line, 716: transistor, 717: transistor, 718: liquid crystal        element, 719: liquid crystal element, 720: pixel, 721: switching        transistor, 722: driver transistor, 723: capacitor, 724:        light-emitting element, 725: signal line, 726: scan line, 727:        power supply line, 728: common electrode, 800: substrate, 810:        introduction port, 820: chamber, 830: light-emitting element,        930: substrate, 931: electrode, 932: electrode, 933: electrode,        934: bridge electrode, 936: electrode, 937: electrode, 938:        intersection portion, 941: wiring, 942: wiring, 950: FPC, 951:        IC, 1700: substrate, 1701: chamber, 1702: load chamber, 1703:        pretreatment chamber, 1704: chamber, 1705: chamber, 1706: unload        chamber, 1711 a: source material supply portion, 1711 b: source        material supply portion, 1712 a: high-speed valve, 1712 b:        high-speed valve, 1713 a: source material introduction port,        1713 b: source material introduction port, 1714: source material        exhaust port, 1715: evacuation unit, 1716: substrate holder,        1720: transfer chamber, 3501: wiring, 3502: wiring, 3503:        transistor, 3504: liquid crystal element, 3510: wiring, 3510_1:        wiring, 3510_2: wiring, 3511: wiring, 3515_1: block, 3515_2:        block, 3516: block, 5100: pellet, 5100 a: pellet, 5100 b:        pellet, 5101: ion, 5102: zinc oxide layer, 5103: particle, 5105        a: pellet, 5105 a 1: region, 5105 a 2: pellet, 5105 b: pellet,        5105 c: pellet, 5105 d: pellet, 5105 d 1: region, 5105 e:        pellet, 5120: substrate, 5130: target, 5161: region, 7101:        housing, 7102: housing, 7103: display portion, 7104: display        portion, 7105: microphone, 7106: speaker, 7107: operation key,        7108: stylus, 7302: housing, 7304: display portion, 7311:        operation button, 7312: operation button, 7313: connection        terminal, 7321: band, 7322: clasp, 7501: housing, 7502: display        portion, 7503: operation button, 7504: external connection port,        7505: speaker, 7506: microphone, 7701: housing, 7702: housing,        7703: display portion, 7704: operation key, 7705: lens, 7706:        joint, 7801: housing, 7802: display portion, 7803: operation        button, 7804: speaker, 7921: utility pole, 7922: display        portion, 8121: housing, 8122: display portion, 8123: keyboard,        8124: pointing device, 9700: automobile, 9701: car body, 9702:        wheel, 9703: dashboard, 9704: light, 9710: display portion,        9711: display portion, 9712: display portion, 9713: display        portion, 9714: display portion, 9715: display portion, 9721:        display portion, 9722: display portion, 9723: display portion.

This application is based on Japanese Patent Application Ser. No.2014-219635 filed with Japan Patent Office on Oct. 28, 2014, the entirecontents of which are hereby incorporated by reference.

The invention claimed is:
 1. A display device comprising: a firstsubstrate; and a second substrate, wherein a first surface of the firstsubstrate is provided with a first insulating layer, wherein a firstsurface of the second substrate is provided with a second insulatinglayer, wherein the first surface of the first substrate and the firstsurface of the second substrate face each other, wherein the firstsubstrate has a second surface opposite to the first surface, whereinthe second substrate has a second surface opposite to the first surface,wherein an adhesive layer is positioned between the first insulatinglayer and the second insulating layer, wherein, in the vicinity of aperipheral portion of the first substrate and the second substrate, aprotective film covers the first surface, a side surface and the secondsurface of the first substrate, a side surface of the adhesive layer,and the first surface of the second substrate, and does not cover a sidesurface of the second substrate, and wherein a portion of the protectivefilm that covers the side surface of the first substrate overlaps andextends past the side surface of the second substrate.
 2. The displaydevice according to claim 1, wherein the protective film is in contactwith the side surface of the first substrate and is not in contact withthe side surface of the second substrate.
 3. The display deviceaccording to claim 1, wherein a transistor, a capacitor, a displayelement, a light-blocking layer, a coloring layer, and a spacer arebetween the first surface of the first substrate and the first surfaceof the second substrate.
 4. The display device according to claim 1,wherein the protective film comprises any one of oxygen, nitrogen and ametal.
 5. The display device according to claim 4, wherein theprotective film comprises one selected from the group consisting ofaluminum oxide, hafnium oxide, zirconium oxide, titanium oxide, zincoxide, indium oxide, tin oxide, indium tin oxide, tantalum oxide,silicon oxide, manganese oxide, nickel oxide, erbium oxide, cobaltoxide, tellurium oxide, barium titanate, titanium nitride, tantalumnitride, aluminum nitride, tungsten nitride, cobalt nitride, manganesenitride, hafnium nitride, ruthenium, platinum, nickel, cobalt, manganeseand copper.
 6. The display device according to claim 2, wherein theprotective film is not in contact with the second surface of the secondsubstrate.
 7. The display device according to claim 3, wherein thedisplay element is a liquid crystal element.
 8. The display deviceaccording to claim 3, wherein the display element is an organic ELelement.
 9. An electronic device comprising: the display deviceaccording to claim 1; and a microphone or a speaker.
 10. A method formanufacturing a display device, comprising the steps of: forming atransistor and a first insulating layer over a first surface of a firstsubstrate; bonding the first substrate and a second substrate with anadhesive layer in a manner that the first surface of the first substrateand a first surface of the second surface face each other; forming agroove portion by performing a first cutting treatment on the secondsubstrate after bonding the first substrate and the second substrate;and forming a protective film in the vicinity of a peripheral portion ofthe first substrate and the second substrate after forming the grooveportion, the protective film being in contact with the first substrate,the adhesive layer and the second substrate in the vicinity of thegroove portion.
 11. The method for manufacturing a display deviceaccording to claim 10, wherein the protective film is in contact withthe first surface of the first substrate and a second surface of thefirst substrate, and wherein the second surface of the first substrateis an opposite surface of the first substrate to the first surface ofthe first substrate.
 12. The method for manufacturing a display deviceaccording to claim 10, wherein the protective film is formed by anatomic layer deposition method.
 13. The method for manufacturing adisplay device according to claim 10, wherein the protective filmcomprises one selected from the group consisting of aluminum oxide,hafnium oxide, zirconium oxide, titanium oxide, zinc oxide, indiumoxide, tin oxide, indium tin oxide, tantalum oxide, silicon oxide,manganese oxide, nickel oxide, erbium oxide, cobalt oxide, telluriumoxide, barium titanate, titanium nitride, tantalum nitride, aluminumnitride, tungsten nitride, cobalt nitride, manganese nitride, hafniumnitride, ruthenium, platinum, nickel, cobalt, manganese and copper. 14.The method for manufacturing a display device according to claim 11,wherein the protective film is not in contact with a second surface ofthe second substrate, and wherein the second surface of the secondsubstrate is an opposite surface of the second substrate to the firstsurface of the second substrate.